View source for The Encyclopedia Americana (1920)/Mineralogy

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'''MINERALOGY''' is the science which
treats of minerals and especially of the
properties of these minerals, their chemical
behavior and composition, their crystalline form
and structure, their physical characters, their
classification and their determination. Mineralogy
also considers the part each mineral plays
in Nature, its history, its formation and alterations,
its variations under different conditions
and its relation to other minerals. From a
practical standpoint it records the uses of each
mineral and the localities in which it has been
found.

Mineralogy has many connections with other
sciences, especially with crystallography and
geology, for minerals are crystals for the most
part and must be studied as such, and rocks
are only aggregates of minerals and are identified
by study of the component minerals.
Physics, chemistry and mathematics are
fundamental in the study of minerals and minerals
are the raw material of the chemist and used
by the physicist for the establishment of physical
laws. Finally the arts of mining and metallurgy
are concerned, the one with the extraction
of minerals from the earth, the other with
the extraction of metals from minerals.

Minerals arc those substances of definite
chemical composition which are found ready
made in the crust of the earth and are not
directly products of the life or decay of an
organism. Usually also they will exhibit definite
and characteristic molecular (crystalline)
structures.

Although minerals constitute the larger
portion by far of the known so-called mineral
kingdom, the definition excludes certain
portions. Lack of homogeneity excludes asphalt
and petroleum; lack of definite chemical
composition excludes the natural glasses; ice made
in the factory and ruby made in the furnace
are not minerals. Coral and pearl are direct
products of organic life, therefore not
minerals.

The fundamental requirement of definite
chemical composition is sometimes apparently
waived because other facts, especially proof of
definite crystalline structure, have been obtained,
although a satisfactory formula has not. For
<!-- column 2 -->
instance, it is not yet possible to state an
unobjectionable formula for tourmaline, and the
formulas of the great triclinic feldspars were
long a source of confusion. The reasons are
manifold, faulty analysis, impurities, replac<ins>e</ins>ments
of one element or group by another, and
sometimes, as in the so-called colloid minerals,
the originally formed material has taken out
other things from solutions which in the dried-out
mineral remain inextricably admixed.

The characteristic crystalline structure is so
frequent that minerals are sometimes defined as
natural crystals. But it is now recognized that
crystallinity is dependent on conditions during
or preceding solidification, and that, theoretically,
like any other chemical substance a
mineral may, under different conditions, form in
the crystalline state or the amorphous state.
Not only is this theoretically true, but there are
many so-called &ldquo;gel&rdquo; minerals which are known
only in the amorphous state and other minerals
which are known both in the amorphous and
the crystalline state.

Historically, mineralogy as a science dates
from the 18th century only. While the ancients
utilized a very considerable number of minerals,
some for the metals they contained, others as
pigments, others as ornaments, charms and
talismans and still others in medicine and the
arts, they knew little as to their composition
and nothing as to their molecular structure.
They classified them, it is true, for there is still
extant part of a work, &lsquo;On Stones,&rsquo; written by
Theophrastus, who died 286 {{smaller|B.C.}}, while Pliny in
his great work on natural history, published
77 {{smaller|A.D.}}, devotes five books to &ldquo;earths, metals,
stones and gems.&rdquo;

The greatest contribution to mineralogical
knowledge prior to the 18th century was made
by Georg Agricola (1494-1555), professor of
chemistry at Chemnitz, Saxony, who minutely
discussed the known important ores, their mining,
concentration and metallurgy; and may be
said to have summed up and systematized the
knowledge of minerals at that period.

As chemical knowledge increased the
compositions of minerals were gradually determined
and chemical tests began to replace arbitrary
distinctions of structure, color and the like.
This is clearly shown in the works of Wallerius,
1747, and Werner, 1798; and from this time the
composition became the dominating character.

The existence of a characteristic crystalline
structure for most minerals was very gradually
recognized and, until the publication of the
works of Romè de l'Isle in 1783 and Rènè Just
Haüy (who &ldquo;raised mineralogy to the rank of
a science&rdquo;), played no part in the study of
minerals. From this period the fundamental
importance of the crystalline structure and the
part it plays in the interpretation of both physical
and chemical phenomena have been everywhere
recognized.

Mineralogy may conveniently be considered
under the following headings: (1) Crystallography;
(2) Physical Mineralogy; (3) Chemical
Mineralogy; (4) Formation and Occurrence;
(5) Uses; (6) Descriptive Mineralogy;
(7) Determinative Mineralogy.


{|align="center" border="1"
|[[Image:Americana 1920 Mineralogy - Crystals.jpg|600px]]
|}

{|align="center" cellpadding="0" cellspacing="0" width="600"
|align="right"|'''9'''
|align="left"|&nbsp;'''Amethyst Crystals in parallel position'''
|'''13'''
|align="left"|&nbsp;'''Cubical&nbsp;cleavage&nbsp;of&nbsp;Halite'''&nbsp;&nbsp;
|-
|'''10'''
|align="left"|&nbsp;'''Reniform Hematite'''
|'''14'''
|align="left"|&nbsp;'''Curved Gypsum'''
|-
|'''11'''
|align="left"|&nbsp;'''Conchoidal fracture of Uintahite'''
|'''15'''
|align="left"|&nbsp;'''Star Sapphire'''
|-
|'''12'''
|align="left"|&nbsp;'''Tree&nbsp;agate&nbsp;showing&nbsp;arborescent&nbsp;form&nbsp;of&nbsp;Wad'''&nbsp;&nbsp;
|'''16'''
|align="left"|&nbsp;'''Reticulated Cerussite'''
|}


'''1. Crystallography'''.—Crystallography,
although a distinct science, has developed with
mineralogy and is so interwoven with it that
the two sciences are usually taught and studied
<!-- p. 165 -->
by the same specialists. Crystallography is
discussed separately in the articles {{Americana article link|Crystals}};
{{Americana article link|Crystallography}};
{{Americana article link|Chemical Crystallography}};
and {{Americana article link|Physical Crystallography}}. The
subject need here be only briefly referred to in
its relation to mineralogical study.

As previously stated most minerals exhibit in
all or some of their occurrences a definite
crystalline structure. If the mineral develops
&ldquo;well faced&rdquo; crystals the geometric symmetry
and constants are obtained by a measurement
of the interfacial angles of these crystals. If
however these plane-faced crystals are lacking
the crystalline structure is studied by the directional
characters: cleavage, behavior with polarized
light, etch figures, thermal and electrical
properties, etc., which yield not only
characteristic constants but often the complete
symmetry.

Aside from these mentioned constants and
symmetry relations resulting from a study of
the crystals, interesting problems arise such as
the relations between composition and crystalline
structure, the causes of variation in crystal
habit, and the reasons for vicinal planes and
parallel growths.

'''2. Physical Mineralogy'''.—Physical mineralogy
considers the physical characters of
minerals. Many of these are crystal characters
since they vary with the direction and have
therefore been discussed in the articles on
{{Americana article link|Crystals}};
{{Americana article link|Crystallography}};
{{Americana article link|Cleavage}}; and
{{Americana article link|Physical Crystallography}}. Other physical
characters, however, which are not dependent
or notably dependent on the direction the test
is made, are, nevertheless, important and some
of these may be described as follows:

''Lustre'', in the mineralogical sense, is not the
degree of brilliancy, but the ''kind'' of brilliancy.
Light reflected from different substances and
quite independently of the color, produces
different effects; one substance resembles a metal,
another glass, another silk, and they are said to
possess respectively metallic lustre, vitreous
lustre and silky lustre. The determining causes
appear to be transparency, structure and
refractive power. The most used terms are:
Metallic lustre exhibited by those opaque
minerals which with the exception of the native
metals have a black or nearly black powder.
Non-metallic lustre exhibited by all transparent
or translucent minerals, which is subdivided into
vitreous, adamantine, resinous, pearly, silky
and waxy according to the similarity in sheen
to glass, diamond, resin, mother of pearl, silk
and wax respectively.

''Color'', by either transmitted or reflected
light, depends upon the power of the
substance to absorb different proportions of the
lights of different wave lengths which together
make up the light used. The same substance
may, therefore, appear of different colors when
viewed with different sources of light; and
some minerals are strikingly different as, for
instance, alexandrite, which by daylight is
bluish to olive green and by lamp or gas light
raspberry red. Color is one of the least
constant mineral characters and varies with
different specimens of the same species. The
variation may be due to a few hundredths of
1 per cent of some organic or inorganic
substance dissolved in the mineral, or to larger
amounts of mechanically included foreign {{hyphenated word start|mate|material.}}
<!-- column 2 -->
{{hyphenated word end|rial.|material.}} Color effects may also be due to
interference of light, usually as a result of some
imperfection in the substance, or, in cut stones,
from some purposely chosen shape producing
notable dispersion of the white light into its
component colors. Such effects are known as
play of color, iridescence, opalescence, asterism,
etc.

''Streak'', is the color of the fine powder of
the mineral and is nearly constant, no matter
how the color of the mass varies.

''Hardness'', to the mineralogist, means the
resistance to abrasion of a smooth surface by
a pointed fragment. It is usually, though very
crudely, determined by comparison with the
following scale introduced by Mohs: (1) Talc;
(2) Selenite; (3) Calcite; (4) Fluorite; (5)
Apatite; (6) Orthoclase; (7) Quartz; (8)
Topaz; (9) Sapphire; (10) Diamond.
Intermediate values are window glass 5.5; jeweler's
file 6.5; zircon 7.5; chrysoberyl 8.5; carborundum
9.5. The more common procedure is to
use pointed fragments of the scale minerals
to scratch smooth surfaces of the mineral
being tested. Sometimes this is more conveniently
reversed and roughly polished plates of
the scale minerals are tried by sharp edges or
points of the mineral. The members of the
scale are not in arithmetical ratio. The average
of five attempted comparisons from 9 down
give, roughly, sapphire 100, topaz 30, quartz 18,
orthoclase 12, apatite 7, fluorite 3½, calcite 2½,
gypsum ½. The scale, nevertheless, serves a
useful purpose and no convenient substitute has
yet been suggested. Elaborate tests with a
diamond point, loss of weight by grinding with
a standard powder, production of a crack by
impact or pressure have been tried but fail to
agree even approximately.

The ''Specific Gravity'' of a mineral, as of any
other chemical substance, is of first rank as
a test and is a function of the density of the
molecule. As explained in the article
{{Americana article link|Chemical Crystalloqraphy}} comparative molecular
volumes are obtained by dividing the molecular
weights by the specific gravities.

The specific gravity of a substance is
defined as its weight divided by the weight of
an equal volume of distilled water at 4° C.
The range, in varieties of the same species, is
not great and even this is principally due to
actual differences in composition. The value is
usually obtained by means of a delicate balance
provided with attachments for weighing the
substance in water, such as a small wooden
bench to hold a beaker of distilled water above
the scale pan, and a platinum spiral to hold the
specimen. Three weighings are needed:

''W''&nbsp;= weight of the stone. ''S''&nbsp;= weight of
the spiral when suspended from the end of the
balance frame and immersed in the distilled
water. ''W'''&nbsp;= weight of the stone and the spiral
suspended in distilled water.

Then, Sp.&nbsp;Gr.&nbsp;= <math>\frac{W}{S + W - W'}</math>

Instead of absolute weighings, relative
weights may be determined on a scale by the
stretching of a spring as in the Jolly balance
or by the distance the apparatus sinks in water,
as in the hydrometer; the results are
approximate.

Liquids of high specific gravity such as
concentrated solutions of mercuric and potassic
<!-- p. 166 -->
iodide or of silver thallium nitrate, or organic
liquids like bromoform or methylene iodide,
are often used for quick distinctions between
similar appearing substances, one higher in
specific gravity than the liquid, the other lower.
They may also be conveniently used for
certain exact determinations, being equally accurate
for minute fragments and coarser
material. A liquid is chosen which will float the
material; the proper diluent is then stirred in
drop by drop until a stage is reached at which
the substance, if pushed down, will neither sink
nor rise but stay where pushed. The specific
gravity of the liquid may then be determined
either roughly by dropping in fragments of
material of known specific gravity until one is
found which just sinks and another which
floats, the liquid being of a specific gravity
between these; or for more accurate determination
a special balance, such as the Westphal,
may be used.

Numerous other non-directional characters,
some of which, such as fusibility and elasticity,
are susceptible of exact determination, are
approximately expressed by convenient terms.
Fusibility, for instance, is determined in terms
of a scale of seven minerals by comparing the
effect of the blowpipe flame on small fragments
of similar size. Elastic substances are
distinguished as elastic and flexible. Tenacity is
expressed as brittle, sectile, malleable, ductile or
tough. The fracture surface is said to be
conchoidal, even, uneven, splintery; and terms are
used describing taste, odor and the sense of
touch.

Certain characters are limited to a few
minerals rather than exhibited by all. Such
a character is luminescence or the property of
emitting light at ordinary temperatures after
being subjected to some exciting influence, such
as light, friction, X-rays, ultraviolet light or
radium.

'''3. Chemical Mineralogy.'''—Minerals are
either elements or are formed by the uniting of
atoms of different elements in definite proportions
in accordance with the laws of chemistry
and for either identification or classification
their chemical composition is their most
important characteristic

The methods of analyses and the calculation
of formulæ are in general the same as in the
analyses of other definite chemical substances.
Much attention has to be paid to securing
homogeneous material and in general the problem
is complicated by the fact that most
minerals are isomorphous mixtures (or mixed
crystals) rather than simple salts.

True molecular formulæ are not generally
determinable. The empirical formula is calculated
from the analysis. Thus, for instance,
beryl:


{|align="center" cellpadding="0" cellspacing="0"
|
|align="center"|Percentage<br>&nbsp;Composition&nbsp;
|
|align="center"|Atomic<br>&nbsp;Weights&nbsp;
|
|align="center"|&nbsp;Proportionate&nbsp;<br>Number<br>of Groups
|-
|BeO
|align="center"|14.01
|<nowiki>+</nowiki>
|align="center"|&nbsp;25
|=
|align="center"|&nbsp;.56&nbsp;&nbsp;
|-
|Al{{sub|2}}O{{sub|3}}
|align="center"|19.26
|<nowiki>+</nowiki>
|align="center"|102
|=
|align="center"|&nbsp;.189
|-
|SiO{{sub|2}}
|align="center"|66.37
|<nowiki>+</nowiki>
|align="center"|&nbsp;60
|=
|align="center"|1.106
|}


or closely in the ratio 3BeO.Al{{sub|2}}O{{sub|3}}.6SiO{{sub|2}} or,
summing up, Be{{sub|3}}Al{{sub|2}}(SiO{{sub|3}})O{{sub|6}}.
If the material
is an isomorphous mixture, the sum of the
ratios of the replaceable elements or groups is
considered, for instance, in the sphalerite
analysis which follows, the sum of the {{hyphenated word start|propor|proportions}}
<!-- column 2 -->
{{hyphenated word end|tions|proportions}} in which Zn Fe Cd and Pb are found is
1.040 and the S 1.039.


{|align="center" cellpadding="0" cellspacing="0"
|
|align="center" colspan="2"|Percentage
|
|align="center" colspan="2"|Atomic<br>Weight
|
|align="center" colspan="2"|Proportion
|
|
|align="center" colspan="2"|Number<br>of<br>Groups
|-
|S
|align="right"|33
|align="left"|.25
|<nowiki>+</nowiki>
|align="right"|32
|
|=
|align="right"|1
|align="left"|.039
|
|
|align="center"|I
|-
|Zn
|align="right"|50
|align="left"|.02
|<nowiki>+</nowiki>
|align="right"|65
|align="left"|.4
|=
|
|align="left"|.756
|rowspan="4"|{{brace2|4|r}}
|rowspan="4"|1.040
|rowspan="4" align="center"|I
|-
|Fe
|align="right"|15
|align="left"|.44
|<nowiki>+</nowiki>
|align="right"|56
|
|=
|
|align="left"|.276
|-
|Cd
|align="right"|
|align="left"|.30
|<nowiki>+</nowiki>
|align="right"|112
|
|=
|
|align="left"|.003
|-
|Pb
|align="right"|1
|align="left"|.01
|<nowiki>+</nowiki>
|align="right"|207
|
|=
|
|align="left"|.005
|}


Such a composition could be expressed
either by RS or (Zn.Fe.Cd.Pb)S, the letter R
being used to represent a varying group of
isomorphic or equivalent elements, and the
parentheses with periods between the elements
to show that the zinc, iron, etc., ''taken together''
accompany one atom of sulphur.

The question whether the water given off
during heating is due to the destruction of an
acid or basic salt or a hydroxide or is more
loosely held as so-called water of crystallization,
or is present in solid solution or is adsorbed or
adhering atmospheric water, is often difficult to
answer. Carefully worked-out water curves
showing the loss at frequent intervals of
temperature and the rate of loss at each temperature
will often assist the judgment.

The chemical testing of minerals in practice
is very commonly by the so-called &ldquo;blowpipe
tests&rdquo; which possess certain advantages in
speed, minute amounts of material needed and
in directness of application. Usually no
attempt is made to secure a complete qualitative
analysis, but merely to determine the dominating
constituents. Easy tests exist for most of
the common and many of the rare elements,
and while group separations, except for
instance into volatile and non-volatile, are not
practicable the order of testing is such that
certain elements are detected and largely
removed before the tests for the others are
made.


{|align="center" border="1"
|[[Image:Americana 1920 Mineralogy - Valuable Minerals.jpg|600px]]
|}

{|align="center" width="600"
|align="left"|{{smaller|{{small-caps|copyright, 1912, by f. e. wright.}}}}
|-
|align="center"|VALUABLE MINERALS AS THEY ARE FOUND
|}


'''4. The Formation and Occurrence of'''
'''Minerals'''.—The history of a mineral, the rôle it
has played, is largely told by its occurrence,
associates and alterations, and these facts are
often illuminated by the successful reproduction
of a mineral by a method which does not
conflict with the known natural conditions. The
processes of mineral formation may be broadly
grouped under the headings:

(1) Crystallization from a fluid magma
consisting chiefly of silicates but partly of oxides,
sulphides, fluorides and ferrates mutually
dissolved in each other with certain volatile
constituents, chiefly water. By far the greater
portion of the earth's crust has formed from such
magmas and a comparatively few mineral
groups are found to dominate them. Clarke's
estimate<ref>
Bulletin 491, United States Geological Survey, p. 31.
</ref> is


{|align="center" cellpadding="0" cellspacing="0"
|align="left"|1. The feldspars
|align="right"|59.5
|align="left"|&nbsp;per
|align="left"|&nbsp;cent.
|-
|align="left"|2.&nbsp;The&nbsp;pyroxenes&nbsp;and&nbsp;amphiboles&nbsp;
|align="right"|16.8
|align="center"|&ldquo;
|align="center"|&ldquo;
|-
|align="left"|3. Quartz
|align="right"|12.0
|align="center"|&ldquo;
|align="center"|&ldquo;
|-
|align="left"|4. The micas
|align="right"|3.8
|align="center"|&ldquo;
|align="center"|&ldquo;
|-
|align="left"|5. Accessory minerals
|align="right" style="border-bottom-style: solid; border-bottom-width: thin"|7.9
|align="center"|&ldquo;
|align="center"|&ldquo;
|-
|
|align="right" style="border-bottom-style: double"|100.0
|align="center"|&ldquo;
|align="center"|&ldquo;
|}


The estimated 7 per cent of accessory includes
rarer silicates, elements, sulphides and oxides,
sometimes in quantities which are of economic
value, especially when they have undergone a
natural concentration known as magmatic {{hyphenated word start|segre|segregation,}}
<!-- p. 167 -->
{{hyphenated word end|gation,|segregation,}} as in the important nickel ores of
Sudbury, Canada.

(2) Formation by pneumatolysis, that is
processes in which gases and vapors especially
steam, hydrofluoric, boric, su<ins>l</ins>phuric and
hydrochloric add play a principal part. These gases
and vapors are released by the cooling magmas
and when charged with dissolved matter deposit
it later as new minerals in pegmatite veins,
contacts, tin lodes and other places to which they
may penetrate. These vapors dissolve, transport
and concentrate minerals rare in the rocks
which they penetrate; they form new species
into the composition of which they enter and
they serve as &ldquo;mineralizers,&rdquo; apparently with
catalytic action.

(3) Crystallization or precipitation from
aqueous solutions. Rain water carrying oxygen
and the underground waters with dissolved
carbon dioxide and other constituents are the
chief agents in the disintegration and alteration
of the minerals which are at or near the
surface. They take away selectively much of
the soda, potash and lime and much less of the
magnesia and alumina and silica. The
solutions due to this &ldquo;weathering&rdquo; are in part
redeposited as cements, in part precipitated in the
residual minerals, but much is carried away to
rivers, lakes or oceans, and there may form
deposits of new minerals, such as carbonate of
lime in rivers or underground channels, salt or
other minerals of soda in lakes (or if boric
acid has been present borates may form) and
in land-locked basins, great beds of anhydrite,
gypsum and common salt, or, more rarely, as at
Stassfurt, salts of potassum and magnesium.

The minerals of veins by their composition
and arrangement are shown to be deposits from
watery solution, but in most cases not simply
solutions of the neighboring rocks in the
underground water, but also solutions in the vapors
of deep-seated magmas. As the vapors rise
into regions of lower pressure and temperature
condensation takes place, fluid solutions
form, various species separate and are
deposited on the walls and may ultimately fill the
fissure, forming a vein.

Animal and vegetable organisms often assist
in the formation of minerals from watery
solutions. The original deposits may not always be
strictly mineral species as with coral, shells,
diatomaceous earth, but directly or indirectly
true species often result, such as limonite,
apatite, sulphur and soda nitre. The formation
of a mineral may involve very complex agencies
such as the combined action of intense pressure
from rock folding and of circulating waters
often hot and charged with many constituents,
including the so-called mineralizing agents.
The new minerals are often denser than the
originals and many contain constitutional water.

'''5. The Uses of Minerals.'''—The mineral
industry of this country ranks next to the
agricultural, and the value of the minerals considerably
exceeds $2,000,000,000 a year. While the
principal value of these minerals is for the
extraction of particular constituents such as the
metals or the substances of use in the chemical
industries, there is a large use of the minerals
in their natural state not only as constituents
of building stones, but as abrasives, fertilizers,
fluxes, pigments, refractory materials and in
the making of pottery, porcelain, glass, etc.
Minerals susceptible of polish and with any
<!-- column 2 -->
claim to beauty are utilized as precious or
ornamental stones.

Minerals are the raw material from which
all the metals and all the chemical salts except
the organic compounds are made. Not all
minerals containing a desired element are
utilized, and generally only one or two materials
are obtained ''directly'' from a mineral. These
products are themselves used for the
manufacture of others, as for instance the mineral
halite or common salt is the indirect source of
nearly all of the sodium salts, but is the direct
source principally of a crude sodium sulphate
from which a multitude of other sails are
manufactured.

'''6. Descriptive Mineralogy'''.—It may be
said that it is the province of descriptive
mineralogy to sum up all the results of the study
of minerals, as already outlined, into orderly
form for each mineral species and to so classify
the different species that related minerals shall
be grouped together.

The basis of classification may be scientific,
or economic or genetic; each for certain
purposes being the most satisfactory. Classifications
until the 18th century were based on
distinctions of structure, color, use, or some fancied
similarity, and as has been said were &ldquo;chiefly
designed to enable amateurs to arrange their
collections in a fixed order.&rdquo; Pliny the
naturalist (23-79 {{smaller|A.D.}}) classified as metals earths,
stones and gems. Avicenna nearly 1,000 years
later used a very similar classification with
many subdivisions based on either external
characteristics or easily ascertained properties.

Scientific classifications based on essential
characters began as the increased chemical
knowledge brought composition and chemical
tests to the front. This was instanced in the
systems of Wallerius in 1747 and Werner in
1798. The still later realization that most
minerals possessed a characteristic molecular structure
revealed by its crystals and physical
characters followed naturally the discoveries of
de l'Isle, Haüy and others of the laws governing
crystals; and the methods of examining
crystals placed crystalline structure alongside
chemical composition as the bases of natural
scientific classification. The system of James
D. Dana is probably most used throughout the
world and &ldquo;follows first the chemical composition
and second the crystallographic and other
physical characters which indicate more or less
clearly the relations of individual species.&rdquo;
Eight principal divisions are made from a
chemical standpoint as follows:


{|align="center" cellpadding="0" cellspacing="0"
|align="right" valign="top"|I.
|align="left" width="90%"|&nbsp;''Native Elements.''
|-
|align="right" valign="top"|II.
|align="left"|&nbsp;''Sulphides, Selenides, Tellurides, Arsenides, Antimonides.''
|-
|align="right" valign="top"|III.
|align="left"|&nbsp;Sulpho-salts.&mdash;''Sulpharsenites, Sulphantimonites, Sulphobismuthites.''
|-
|align="right" valign="top"|IV.
|align="left"|&nbsp;Haloids.&mdash;''Chlorides, Bromides, Iodides, Fluorides.''
|-
|align="right" valign="top"|V.
|align="left"|&nbsp;''Oxides.''
|-
|align="right" valign="top"|VI.
|align="left"|&nbsp;Oxygen Salts.<br>1.&nbsp;''Carbonates.'' 2.&nbsp;''Silicates, Titanates.'' 3.&nbsp;''Niobates, Tantalates.'' 4.&nbsp;''Phosphates, Arsenates, Vanadates, Antimonates, Nitrates.'' 5.&nbsp;''Borates, Uranates.'' 6.&nbsp;''Sulphates, Chromates, Tellurates.'' 7.&nbsp;''Tungstates, Molybates.''
|-
|align="right" valign="top"|VII.
|align="left"|&nbsp;Salts of Organic Acids.&mdash;''Oxalates, Mellates, etc.''
|-
|align="right" valign="top"|VIII.
|align="left"|&nbsp;''Hydrocarbon Compounds.''
|}


In subdividing, the chemical composition and
crystalline form are considered with the
purpose of assembling in groups those minerals
which have analogous compositions and closely
similar forms. For instance the barite group
<!-- p. 168 -->
under anhydrous sulphates consists of sulphates
in which Ba, Ca, Sr and Zn are in the same
Mendeléeff group, and which show close
similarity in crystal constants.


{|align="center" cellpadding="0" cellspacing="0"
|
|align="center"|ă
|&nbsp;
|&nbsp;b&nbsp;
|&nbsp;
|align="center"|c'
|-
|align="left"|Barite BaSO{{sub|4}}
|0.8152
|
|align="center"|1
|
|1.3136
|-
|align="left"|Celestite SrSO{{sub|4}}
|0.7790
|
|align="center"|1
|
|1.2801
|-
|align="left"|Anglesite PbSO{{sub|4}}
|0.7852
|
|align="center"|1
|
|1.2894
|-
|align="left"|Anhydrite CaSO{{sub|4}}
|0.8933
|
|align="center"|1
|
|1.0008
|-
|align="left"|Zinkosite ZnSO{{sub|4}}
|0.8925
|
|align="center"|1
|
|1.4137
|-
|align="left"|Hydrocyanite CuSO{{sub|4}}&nbsp;
|style="border-bottom-style: double"|0.7971
|
|align="center" style="border-bottom-style: double"|1
|
|style="border-bottom-style: double"|1.1300
|}


Descriptive mineralogy also serves to keep
in order the nomenclature. Uniformity can
only be obtained if after careful consideration
the term entitled to priority and otherwise
satisfactory is made the name of the species
and the host of synonyms and often unessential
variety names assembled under it.

'''7. Determinative Mineralogy.'''—This
subject has already been discussed in a separate
article. See {{Americana article link|Determinative Mineralogy}}.

'''Bibliography'''.&mdash; The following is a partial
list of comparatively recent works and may be
supplemented by the lists following the articles
on Crystals and Crystallography.

{{sc|Treatises, Mineralogy.}}—Dana, J. D., &lsquo;System
of Mineralogy&rsquo; (6th ed., with three
appendices, 1899, 1909 and 1915, New York 1892);
Hintze, Carl, &lsquo;Handbuch der Mineralogie&rsquo; (Bd.
I, 1904; Bd. 11, 1897, Leipzig; still incomplete).

{{sc|Textbooks, Mineralogy.}}—Bauer, M., &lsquo;Lehrbuch
der Mineralogie&rsquo; (2d ed., Stuttgart
1904); Dana-Ford, &lsquo;Manual of Mineralogy&rsquo;
(13th ed., New York 1912); Dana, E. S., &lsquo;A
Textbook of Mineralogy&rsquo; (New York 1907);
Moses, A. J., and Parsons, C. L., &lsquo;Mineralogy,
Crystallography and Blowpipe Analysis&rsquo; (5th
ed.. New York 1916); Miers, H. A., &lsquo;Mineralogy.
An Introduction to the Scientific Study of
Minerals&rsquo; (London 1902); Naumann-Zirkel,
&lsquo;Elemente der Mineralogie&rsquo; (13th ed., Leipzig
1898); Phillips, A. H., &lsquo;Mineralogy&rsquo; (New
York 1912); Rogers, A. F., &lsquo;Introduction to
the Study of Minerals&rsquo; (New York 1912);
Tschermak, G., &lsquo;Lehrbuch der Mineralogie&rsquo;
(6th ed., 1905).

{{sc|Determinative Mineralogy and Blowpipe
Analysis}}.— Brush-Penfield, &lsquo;Manual of
Determinative Mineralogy&rsquo; (16th ed., New York
1906); Eakle, A. S., &lsquo;Mineral Tables&rsquo; (New
York 1904}; Fuchs-Brauns, &lsquo;Anleitung zum
Bestimmen der Mineralien&rsquo; (6th ed., Giessen
1913); Frazer-Brown, &lsquo;Tables for the
Determination of Minerals&rsquo; (6th ed., Philadelphia
1910); Kraus-Hunt. &lsquo;Tables for the
Determination of Minerals&rsquo; (New York 1911);
Lewis, J. V., &lsquo;Determinative Mineralogy&rsquo; (2d
ed., New York 1915); Plattner-Kolbeck
&lsquo;Probierkunst mit der Lötrohre&rsquo; (7th ed., Leipzig
1907).

{{sc|Chemical Mineralogy}}.—Brauns, R.,
&lsquo;Chemische Mineralogie&rsquo; (Leipzig 1896); Doelter,
C., &lsquo;Physikalische-Chemische Mineralogie&rsquo;
(Leipzig 1905); Doelter, C, &lsquo;Handbuch der
Mineral Chemie&rsquo; (Bd. I, II, III, Dresden
1912-13).

{{sc|Occurrence, Association and Origin of
Minerals}}.—Beyschlag-Krusch-Vogt (trans. by
S. J. Truscott), &lsquo;The Deposits of the Useful
Minerals and Rocks&rsquo; (Vol. I, 1914; Vol. II,
1916; Vol. III, London); Clarke, F. W., &lsquo;The
Data of Geochemistry&rsquo; (Bulletin No. 660,
United States Geological Survey, 1915); Leith
and Meade, &lsquo;Metamorphic Geology&rsquo; (New
<!-- column 2 -->
York 1915); Lindgren, W., &lsquo;Mineral Deposits&rsquo;
(New York 1913); Pirrson, L. V., &lsquo;Rocks and
Rock Minerals&rsquo; (New York 1908); Van Hise,
C. R., &lsquo;A Treatise on Metamorphism&rsquo;
(Monograph 47, United States Geological Survey,
1904); Weinschenck, E., &lsquo;Grundzüge der
Gesteinkünde&rsquo; (Freiburg im Briesgau 1905).

{{sc|Rock Minerals and their Microscopic
Examination}}.—Daly, R. A., &lsquo;Igneous Rocks and
their Origin&rsquo; (New York 1914); Iddings, J. P.,
&lsquo;Rock Minerals&rsquo; (2d ed, New York 1912);
Johannsen, A., &lsquo;Determination of Rock Forming
Minerals&rsquo; (New York 1908); Johannsen, A.,
&lsquo;Manual of Petrographic Methods&rsquo; (New
York 1914); Luquer, L. McI., &lsquo;Minerals in
Rock Sections&rsquo; (4th ed., New York 1913);
Weinschenck-Clark, &lsquo;Petrographic Methods&rsquo;
(New York 1912); Wright, F. E., &lsquo;The Methods
of Petrographic-Microscopic Research&rsquo;
(Carnegie Institution 1911).

{{sc|Microscopic Study of Minerals}}.{{&mdash;
Murdoch, J., &lsquo;Microscopical Determination of the
Opaque Minerals&rsquo; (New York 1916): Schroeder
van der Kolk, J. L. C., &lsquo;Tabellen zur
mikroskopischen Bestimmung der mineralien nach
ihren Brechnungsexponenten&rsquo; (2d ed.,
Wiesbaden 1906); Seeman, F., &lsquo;Leitfaden der
Mineralogischen Bodenanalyse&rsquo; (1914); Winchell-Winchell,
&lsquo;Elements of Optical Mineralogy&rsquo;
(New York 1908).

{{sc|Rare Minerals}}.—Cahen and Wootten,
&lsquo;The Mineralogy of the Rarer Metals&rsquo;
(Philadelphia 1912).

{{sc|Gems and Precious Stones}}.—Bauer, Max,
&lsquo;Edelsteinkunde&rsquo; (2d ed., Leipzig); Cattelle,
W. R., &lsquo;Precious Stones&rsquo; (Philadelphia 1903);
Crookes, Sir Wm., &lsquo;Diamonds&rsquo; (New York
1909); Escard, J., &lsquo;Les Pierres Précieuses&rsquo;
(Paris 1914); Farrington, O. C., &lsquo;Gems and
Gem Minerals&rsquo; (Chicago 1903); Eppler, A.,
&lsquo;Die Schmuck and Edelsteine&rsquo; (Stuttgart
1912); Smith, G. F. H., &lsquo;Gem Stones&rsquo; (New
York 1912).

{{sc|The Uses of Minerals}}.—Dammer und
Tietze, &lsquo;Die Nutzbaren Mineralien&rsquo; (2 vols.,
Stuttgart 1913); &lsquo;Mineral Resources of the
United States&rsquo; (Annually since 1883. U. S.
Geol. Survey); &lsquo;The Mineral Industry&rsquo; (Annually
since 1892. New York); ''Engineering and''
''Mining Journal'', especially Annual Review
number.

{{sc|History of Mineralogy}}.—Fletcher, L.,
&lsquo;Guide to Mineral Collection of British
Museum&rsquo;; v. Kobell, F., <ins>&lsquo;</ins>Geschichte der Mineralogie&rsquo;
(München 1864).

{{sc|Mineral Synonyms}}.—Chester, A. H.,
&lsquo;Dictionary of the Names of Minerals&rsquo; (New York
1896).

{{Americana Author|Alfred J. Moses|label=Professor of Mineralogy, Columbia University}}

{{rule|15%|align=left}}
<references/>