ANORTHIC

SERIES  . Aenigmatite . Na4Fe"9A1 Fe"' (Si,Ti)12044 . Of these, tremolite, hornblende and crocidolite, as well as the important varieties, asbestos and jade, are treated under their own headings . Brief mention only need be here made of some of the others . Naturally, on account of the wide variations in chemical composition, the different members vary considerably in characters and general appearance; the specific gravity, for example, varies from 2•9 in tremolite to 3.8 in aenigmatite . Anthophyllite occurs as brownish, fibrous or lamellar masses with hornblende in mica-schist at Kongsberg in Norway and some other localities . An aluminous variety is known as gedrite, and a deep green, Russian variety containing little iron as kupfferite . Actinolite is an important member of the monoclinic series, forming radiating groups of acicular crystals of a bright green or greyish-green colour . It occurs frequently as a constituent of crystalline schists . The name (from aKTis, a ray, and XiOos, a stone) is a translation of the old German word Strahlstein, radiated stone . Glaucophane, crocidolite, riebeckite and arfvedsonite form a somewhat special group of alkali-amphiboles .

The two former are

blue fibrous minerals occurring in crystalline schists, and are the result of dynamo-metamorphic processes; the two latter are dark green minerals which occur as original constituents of igneous rocks rich in soda, such as nepheline-syenite and phonolite . Aenigmatite and its variety cossyrite are rare minerals forming constituents of igneous rocks of the nepheline-syenite and phonolite groups . (L . J .