Basalt. Chiefly augite—an intimate mixture of augite and felspar with magnetic iron, olivine, &c. See [p. 371.] The yellowish green mineral called olivine, can easily be distinguished from yellowish felspar by its infusibility, and having no cleavage. The edges turn brown in the flame of the blow-pipe.
Basanite. Name given by Alex. Brongniart to a rock, having a base of basalt, with more or less distinct crystals of augite disseminated through it.
Claystone and Claystone-porphyry. An earthy and compact stone, usually of a purplish colour, like an indurated clay; passes into hornstone; generally contains scattered crystals of felspar and sometimes of quartz.
[Clinkstone]. Syn. Phonolite, fissile Petrosilex; a greenish or greyish rock, having a tendency to divide into slabs and columns; hard, with clean fracture, ringing under the hammer; principally composed of compact felspar, and, according to Gmelin, of felspar and mesotype. (Leonhard, Mineralreich, p. 102.) A rock much resembling clinkstone, and called by some Petrosilex, contains a considerable percentage of quartz and felspar. As both trachyte and basalt pass into clinkstone, the rock so called must be very various in composition.
Compact Felspar, which has also been called Petrosilex; the rock so called includes the hornstone of some mineralogists, is allied to clinkstone, but is harder, more compact, and translucent. It is a varying rock, of which the chemical composition is not well defined, and is perhaps the same as that of clay. (MacCulloch's Classification of Rocks, p. 481.) Dr. MacCulloch says, that it contains both potash and soda.
Cornean. A variety of claystone allied to hornstone. A fine homogeneous paste, supposed to consist of an aggregate of felspar, quartz, and hornblende, with occasionally epidote, and perhaps chlorite; it passes into compact felspar and hornstone. (De la Beche, Geol. Trans. second series, vol. 2. p. 3.)
[Diallage rock]. Syn. Euphotide, Gabbro, and some Ophiolites. Compounded of felspar and diallage, sometimes with the addition of serpentine, or mica, or quartz. (MacCulloch. ibid. p. 648.)
Diorite. A kind of [greenstone], which see. Components, felspar and hornblende in grains. According to Rose, Ann. des Mines, tom. 8. p. 4., diorite consists of albite and hornblende.
Dioritic-porphyry. A porphyritic greenstone, composed of crystals of albite and hornblende, in a greenish or blackish base. (Rose, ibid. p. 10.)
Dolerite. Formerly defined as a synonym of [greenstone], which see. But, according to Rose (ibid. p. 32.), its composition is black augite and Labrador-felspar; according to Leonhard (Mineralreich, &c. p. 77.), augite, Labrador-felspar, and magnetic iron.