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:

OrderI. 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:

Section1. 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

Suborder1. 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′.

Rang1. 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