Ch. 3: Precious Gem stones in 1905

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	PRECIOUS STONES.	1353

	Arizona.—At Clip, Ariz., the associated mineral is kyanite; so that these three species, so nearly allied in composition, appear to have close relation with the dumortierite, one or other of the group being in every case associated. The bearing of this fact will be noted presently. Muscovite, also in small quantities and apparently a product of alteration, is present at each of these three western localities. At the New York occurrence, in Harlem, the dumortierite appears in a vein of coarse red pegmatite, and is generally in the feldspar, associated with black tourmaline, muscovite, and small quantities of some other minerals. The French localities near Lyons present a similar mode of occurrence. At a few points in Bohemia and Silesia it is also known, and appears to belong in a pegmatite. Mr. Sehaller's paper goes into a very careful examination to determine the exact composition of this species and its proper place among the silicates. The analysis brings out very clearly the true constitution of dumortierite as a member of the kyanite-sillimanite-andalusite group, differing from andalusite only in a small content of boron. The average of the two analyses of Dehesa material is as follows:



	This, when written graphically, is extremely close to the expression for andalusite, the radical BO, with a hydrogen atom, replacing a part of the alumina. The alteration of dumortierite to muscovite is also shown very readily, alumina and boric acid being set free and potash taken up. As to the physical properties of dumortierite. the crystallization is ortho-rhombic, though there is little material to judge precisely upon, the mineral being usually fibrous. The density averages 3.3. Pleochroism is marked and varies in specimens from different localities, being colorless (or rarely pale yellow) to cobalt blue, pistachio green, rose salmon, carmine or red-purple— the latter is found only in the California specimens, and is regarded by Mr. Schaller as due to the titanium present. LEPIDOLITE. In the eighteenth century lepidolite was used as a pleasing ornamental stone, polished and cut into such objects as are fluorite and malachite. In a series of mineralogical notes in Bulletin No. 262 of the United States Geological Survey, Mr. W. T. Schaller describes some features of the crystallization of lepidolite." He has examined a number of crystals from the vicinity "Schaller, W. T., Contrib. to Mineralogy: Bull. U. S. Geol. Survey No. 262, 1905, pp. 130-U3.

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