These ratios are used throughout the system. In (1) A is extreme; in (5) B is extreme; in (2) A dominates over B; in (4) B dominates over A; in (3) A and B are equal or nearly equal.

All igneous rocks are grouped in five (5) primary divisions called Classes on a basis of the proportions of the salic and femic minerals, thus:

Class	I.	Sal   7 ——  >  —, extremely rich in salic minerals, called persalane. Fem   1
	II.	Sal   7   5 ——  <  —  >  —, with dominant salic minerals, called dosalane. Fem   1   3
	III.	Sal   5   3 ——  <  —  >  —, salic and femic minerals, equal or nearly equal, called salfemane. Fem   3   5
	IV.	Sal   3   1 ——  <  —  >  —, with dominant femic minerals, called dofemane. Fem   5   7
	V.	Sal   1 ——  <  —, extremely rich in femic minerals, called perfemane. Fem   7

Each of these classes is divided into two subclasses according to the proportions of two subgroups of the preponderant group of standard minerals. Of salic minerals one subgroup includes quartz, feldspars, and the feldspathoids; the other includes corundum and zircon. Of femic minerals one subgroup includes the silicates with magnetite, ilmenite, hematite, and rutile; the other contains apatite and the remaining minerals of this group. Most known igneous rocks fall into the first subclass of each class.

The classes are further divided into orders according to the proportions of certain minerals in the preponderant subgroups. Thus Classes I, II, and III are each divided into nine orders on a basis of the proportions of quartz and the feldspars, and of the feldspars and the feldspathoids, quartz and feldspathoids not occurring together. The orders may be described in the same terms for each of the first three classes as follows:

Order	I.	Q   7 —  >  —, extremely rich in quartz, perquaric. F   1
	II.	Q   7   5 —  <  —  >  —, quartz dominant over feldspar, doquaric. F   1   3
	III.	Q   5   3 —  <  —  >  —, quartz and feldspar equal or nearly equal, quarfelic. F   3   5
	IV.	Q   3   1 —  <  —  >  —, feldspar dominant over quartz, quardofelic. F   5   7
	V.	Q or L   1 ———  <  —, extremely rich in feldspar, perfelic. F   7
	VII.	L   5   3 —  <  —  >  —, feldspar and lenads equal or nearly equal, lenfelic. F   3   5
	VIII.	L   7   5 —  <  —  >  —, lenads dominant over feldspars, dolenic. F   1   3
	IX.	L   7 —  >  —, extremely rich in lenads, perlenic. F   1

In classes IV and V the preponderant minerals are femic, and in subclass 1 they are silicates, titanates, and ferrates, with hematite and rutile. These are subdivided as follows:

Silicates—pyroxenes and olivine with akermanite in one subgroup; the other minerals, magnetite, hematite, ilmenite, titanite, perofskite, rutile, in the second subgroup. This first group is called polic, mnemonic of pyroxene and olivine; the second group is called mitic, mnemonic of magnetite, ilmenite, titanite.

There are five orders in each of these classes, as follows:

Order	I.	PO   7 —  >  —, extremely rich in pyroxene or olivine, perpolic. M   1
	II.	PO   7   5 —  <  —  >  —, dominant pyroxene or olivine, dopolic. M   1   3
	III.	PO   5   3 —  <  —  >  —, pyroxene or olivine, equal or nearly equal to the mitic minerals, polmitic. M   3   5
	IV.	PO   3   1 —  <  —  >  —, dominant mitic minerals, domitic. M   5   7
	V.	PO   1 —  <  —, extremely rich in mitic minerals, permitic. M   7

In the first three orders a distinction between pyroxene and olivine is recognized by sections, five in number:

Section	1.	P   7 —  >  —, extremely rich in pyroxene, perpyric. O   1
	2.	P   7   5 —  <  —  >  —, dominant pyroxene, dopyric. O   1   3
	3.	P   5   3 —  <  —  >  —, pyroxene and olivine, equal or nearly equal, pyrolic. O   3   5
	4.	P   3   1 —  <  —  >  —, dominant olivine, domolic. O   5   7
	5.	P   1 —  <  —, extremely rich in olivine, perolic. O   7

In the last two orders a distinction between the preponderant mitic minerals is recognized by suborders, five in number. The minerals containing Fe₂O₃ are compared with those containing TiO₂. The former, magnetite and hematite, are called hemic, mnemonic of hematite; the latter subgroup, titanite, ilmenite, perofskite, rutile, are called tilic, mnemonic of titanite and ilmenite. Of orders 4 and 5, there are

Suborder	1.	H   7 —  >  —, hemic minerals extreme, perhemic. T   1
	2.	H   7   5 —  <  —  >  —, dominant hemic minerals, dohemic. T   1   3
	3.	H   5   3 —  <  —  >  —, hemic and tilic minerals equal or nearly equal, tilhemic. T   3   5
	4.	H   3   1 —  <  —  >  —, dominant tilic minerals, dotilic. T   5   7
	5.	H   1 —  <  —, tilic minerals extreme, pertilic. T   7

Further subdivision, producing rangs and subrangs, is made on the character of the chemical bases in the standard minerals used in forming orders and is expressed in terms of the molecular proportions of certain oxides. For the salic minerals, forming orders in the first three classes, the bases are alkalies—K₂O and Na₂O—and lime, CaO. For the femic minerals, forming orders in the last two classes, the bases are MgO, FeO, CaO and alkalies, K₂O, Na₂O. In classes I, II, and III rangs are formed by comparing salic alkalies, K₂O′ + Na₂O′, with salic lime, CaO′; and subrangs are formed by comparing K₂O′ with Na₂O′.

Rang	1.	K2O′ + Na2O′   7 ——————  >  —, alkalies extreme, peralkalic. CaO′   1
	2.	7   5 “  <  —  >  —, alkalies dominant, domalkalic.     1   3
	3.	5   3 “  <  —  >  —, alkalies and lime equal or nearly so, alkalicalcic.     3   5
	4.	3   1 “  <  —  >  —, lime dominant, docalcic.     5   7
	5.	1 “  <  —, lime extreme, percalcic.     7

Subrang	1.	K2O′   7 ———  >  —, potash extreme, perpotassic. Na2O′   1
	2.	7   5 “  <  —  >  —, potash dominant, dopotassic.     1   3
	3.	5   3 “  <  —  >  —, potash and soda equal, sodipotassic.     3   5
	4.	3   1 “  <  —  >  —, soda dominant, dosodic.     5   7
	5.	1 “  <  —, soda extreme, persodic.     7

In classes IV and V rangs are formed by comparing femic MgO + FeO + CaO″ with femic alkalies K₂O″ + Na₂O″.

Minerals containing magnesia, iron, and lime are called mirlic.

Rang	1.	MgO + FeO + CaO″   7 ————————  >  —, extremely mirlic, permirlic. K2O″ + Na2O″   1
	2.	7   5 “  <  —  >  —, dominantly mirlic, domirlic.     1   3
	3.	5   3 “  <  —  >  —, equally mirlic and alkalic, alkalimirlic.     3   5
	4.	3   1 “  <  —  >  —, dominantly alkalic, domalkalic.     5   7
	5.	1 “  <  —, extremely alkalic, peralkalic.     7

Sections of rangs distinguish between MgO + FeO and CaO″. Minerals with MgO + FeO are called miric.

Section	1.	MgO + FeO   7 —————  >  —, extremely mirlic, permirlic. CaO″   1
	2.	7   5 “  <  —  >  —, dominantly miric, domiric.     1   3
	3.	5   3 “  <  —  >  —, equally miric and calcic, calcimiric.     3   5
	4.	3   1 “  <  —  >  —, dominantly calcic, docalcic.     5   7
	5.	1 “  <  —, extremely calcic, percalcic.     7

Subrangs distinguish between MgO and FeO, thus:

Subrang	1.	MgO   7 ——  >  —, extremely magnesic, permagnesic. FeO   1
	2.	7   5 “  <  —  >  —, dominantly magnesic, domagnesic.     1   3
	3.	5   3 “  <  —  >  —, equally magnesic and ferrous, magnesiferrous.     3   5
	4.	3   1 “  <  —  >  —, dominantly ferrous, doferrous.     5   7
	5.	1 “  <  —, extremely ferrous, perferrous.     7

Finally a recognition of the character of the subordinate standard minerals leads to further subdivisions known as grads and subgrads. They only occur in classes II, III, and IV, because these are the only ones in which the subordinate minerals are in notable amounts. Grads are formed in a manner similar to that employed to produce orders. Thus grads in classes II and III correspond to orders in class IV and the reverse. Subgrads are the same in form as rangs when the difference in the treatment of salic and femic minerals is borne in mind. The names given to these divisions, which in fact recognize only the character of the magma, are derived from geographical localities and embrace many of those already in use, except that the names of orders are taken from countries or nations. Specific terminations indicate the place in the series of divisions:

ane for class, one for subclass.

are for order, ore for suborder.

ase for rang, ose for subrang.

ate for grad, ote for subgrad.

This may be illustrated as follows:

Class I. persalane, all rocks extremely salic.

Order 4. britannare, feldspar dominant over quartz, quardofelic. Many rocks of granitic composition whether crystalline or glassy.

Rang 1. liparase, peralkalic, rocks in which the potential feldspars are extremely alkalic, orthoclase, or albite.

Subrang 2. Omeose, dopotassic, rocks in which the extremely alkali feldspars are dominantly potassic, orthoclase, with subordinate albite. Examples of omeose are: granite from Omeo, Victoria, Australia, and rhyolite from Silver Cliff, Colorado.

The presence of distinctive minerals not indicated in the standard mineral composition of norm is expressed by qualifying the magmatic name by the name of the distinctive mineral; as, a hornblende-monzonose.

The precise texture of the rock is expressed by qualifying the magmatic name by a textural adjective; as, a grano-monzonose, a vitro-monzonose, a phyro-monzonose, etc.

REFERENCE LIST OF THE MORE COMMON MINERALS.

Actinolite—a magnesium-calcium-iron amphibole (q.v.); commonly bright green to grayish green; crystals usually slender or fibrous.

Agate—a banded or variegated chalcedony (quartz, q.v.).

Alabaster—a fine-grained variety of gypsum (q.v.), either white or delicately colored.

Albite—a soda feldspar (q.v.), an aluminum-sodium silicate; H. 5–6; cleavage perfect in two planes; luster vitreous or pearly white; occasionally bluish gray, reddish, greenish; sometimes opalescent.

Amethyst—a variety of quartz of purple or bluish-violet color, due probably to manganese.

Amphibole—the type of an important group of rock-forming minerals known as the amphibole or hornblende group; a ferromagnesian silicate, monoclinic, H. 5–6; luster vitreous to pearly; fibrous varieties often silky; black, ranging through various shades of green to light colors; embraces the magnesium-calcium varieties, tremolite and nephrite; the magnesium-calcium-iron variety actinolite; the aluminous-magnesium-iron-calcium variety hornblende, and others.

Analcite—analcine, one of the zeolites; a hydrous aluminum-sodium silicate; luster vitreous, colorless, white; occasionally grayish, greenish, yellowish, reddish, transparent to opaque.

Andesine—a plagioclase feldspar (q.v.); a sodium-calcium-aluminum silicate, intermediate in composition between albite and anorthite; H. 5–6; white, gray, grayish, yellowish, flesh red; luster subvitreous, inclining to pearly.

Andalusite—an aluminum silicate; luster vitreous; whitish, rose red, flesh red, variety pearly gray, reddish brown, olive-green; H. 7.5, infusible; impurities sometimes so arranged in the interior as to exhibit a colored, crossed, or tesselated appearance in cross-section (chiastolite).

Anhydrite—a calcium sulphate; H. 3–3.5; luster pearly to vitreous; white, sometimes bluish or reddish; differs from gypsum in absence of water and in its greater hardness.

Anorthite—a plagioclase feldspar (q.v.); a calcium-aluminum silicate; varies much by impurities and admixtures; H. 6–6.5; pearly or vitreous luster; white, grayish, reddish.

Anthracite—hard coal; hydrocarbon with impurities; supposed to be derived from bituminous coal by metamorphism.

Antimony—a native metal, tin-white, brittle; rather rare in native form.

Apatite—essentially calcium phosphate with chlorine or fluorine; hexagonal; H. 5; luster vitreous or subresinous; colors usually greenish to bluish, characterized by a hexagonal form.

Aragonite—a calcium carbonate; differs from calcite in cleavage, and in being orthorhombic; H. 3.5–4; luster vitreous or resinous; white, also gray, yellow, green, and violet.

Asphaltum—asphalt; mineral pitch, bitumen; a natural mixture of different hydrocarbons; odor bituminous; melts at 90 to 100 degrees C.; burns with a bright flame; graduates into mineral tars and through these into petroleum; probably the residue of the latter.

Augite—one of the pyroxenes (q.v.); an aluminum-calcium-magnesium-iron silicate; H. 5–6; monoclinic, crystals usually thick and stout; sometimes lamellar; also granular; black, greenish black, deep green; an important rock-forming mineral.

Beauxite—essentially hydrated alumina; occurs in concretionary grains of clay-like form, whitish to brown; valuable as a source of aluminum.

Beryl—a beryllium-aluminum silicate; hexagonal; prismatic; H. 8; luster vitreous or resinous; marl-green, pale passing into whitish; closely resembles apatite, but distinguished by superior hardness and in composition.

Barite—barites, heavy-spar, barium sulphate; orthorhombic, H. 3–3.5; luster vitreous to resinous, sometimes pearly; white, inclining to yellow, gray, blue, red, or brown; very heavy, sp. sr. 4.3–4.7.

Biotite—black mica, a potash-aluminum-magnesium-iron silicate; monoclinic; easy basal cleavage into thin laminæ; sometimes occurs as a massive aggregation of cleavable scales; H. 2.5–3; luster splendent on cleavage surface; black to dark green; cleavage surfaces smooth and shining; a very common constituent of crystalline rocks.

Bitumen—the same as asphaltum (q.v.).

Bismuth—a metal of whitish color and rather brittle nature; occurring occasionally native, usually as an ore.

Bronzite—a variety of enstatite (q.v.); grayish green to olive-green and brown with luster on cleavage surface often adamantine, pearly or bronze-like and submetallic.

Calcite—calcspar; calcium carbonate; rhombohedral, perfect rhombohedral cleavage; often taking the forms known as dogtooth spar, nail-head spar; frequently stalactitic and stalagmitic; H. 2.5–3.5; luster vitreous; white, occasionally pale shades of gray, red, green, blue, violet, yellow, brown; strong double refraction; embraces variety called Iceland spar; a very common mineral; the essential basis of limestone.

Cassiterite—tin stone; an oxide of tin; tetragonal; luster adamantine, usually splendent; brown or black, sometimes red, gray, white, or yellow; an important source of tin.

Catlinite—essentially a hardened red clay, rather a rock than a mineral; much prized by Indians for pipes.

Chalcedony—a cryptocrystalline variety of quartz having a wax-like luster, either transparent or translucent; white, grayish, pale brown to dark brown, black, sometimes delicate blue, occasionally other shades; frequently occurs as the lining or filling of cavities, taking on a botryoidal or mamillary form.

Chiastolite—andalusite (q.v.).

Chlorite—the type of an important group of secondary minerals usually characterized by a green color, softness and smoothness or unctuousness of feeling; they are usually aluminum-magnesium-iron silicates, with chemically combined water; derived from several other species, as pyroxene, amphibole, biotite, garnet, etc.; embraces a number of species, among which are clinochlore, penninite, prochlorite, and delessite.

Chromite—chromic iron; essentially an iron chromate; isometric; luster submetallic; iron black to brownish black; opaque; sometimes magnetic; resembles magnetite.

Chrysolite—olivine; essentially a magnesium-iron silicate; orthorhombic; H. 6–7; luster vitreous; green, commonly olive-green, sometimes yellow, brownish, grayish green; highly infusible; a common constituent of certain basic igneous rocks; the name olivine is more commonly used by geologists.

Chrysotile—a delicately fibrous variety of serpentine (q.v.).

Corundum—alumina; an oxide of aluminum; H. 9; rhombohedral; large crystals usually rough; luster vitreous; color blue, red, yellow, gray, and nearly white; purer forms of fine colors are sapphires; the red variety is ruby, the yellow, oriental topaz, the green, emerald, and the purple, amethyst; dark colors, with iron oxide, emery.

Delessite—a ferruginous chlorite, usually olive-green or blackish green; occurring commonly in the cavities of amygdaloids.

Diallage—a variety of pyroxene (q.v.); H. 4; characterized by thin foliæ; usually grayish green to grass-green, or deep green; luster on cleavage surface pearly, sometimes metalloid or brassy; an essential mineral in the gabbros, as sometimes defined.

Elæolite—a variety of nephelite (q.v.); occurring in large coarse crystals or massive, with greasy luster, from which the name is derived; a characteristic constituent of elæolite syenite.

Enstatite—one of the pyroxenes; essentially a magnesium silicate; orthorhombic; H. 5.5; luster a little pearly on cleavage surface; metalloidal in the bronze variety (bronzite); grayish white, yellowish white, greenish white to olive-green and brown; very infusible; a common mineral in certain basic crystalline rocks.