The principal constituent of insular phosphate rock is a member of the apatite series, usually a carbonate-hydroxyl-fluorine-apatite. Collophane of Sandberger (1870) and Rogers (1917, 1922) is not an amorphous species distinct from apatite. X-ray study of insular and continental phosphate rock, fossil bone and teeth, urinary calculi, and other materials corresponding to collophane, as defined, proves that this substance is a submicrocrystalline variety of apatite, usually carbonate-hydroxyl-apatite, or carbonate-hydroxyl-fluorine-apatite. The name collophane may conveniently be retained as a varietal designation for fine-grained, isotropic, hydrous (and often metacolloidal) types of apatite.

The original specimens of a number of ill-defined, supposed caicium-phosphate species, described by Shepard, Julien, and others, were re-examined by x-ray and optical methods. Ornithite of Julien (1865) is an oriented pseudomorph of carbonate-hydroxyl-apatite after crystals of brushite. Nauruite of Elschner (1913) is identical with carbonate-hydroxyl-fluorine-apatite. The names pyroguanite of Shepard (1856) and sombrerite of Phipson (1862) were applied loosely to ordinary phosphate rock and entirely lack species validity. Type specimens of pyrociasite of Shepard (1856) and of monite of Shepard (1882) were not available, but these materials are doubtless identical with apatite; non-type but probably authentic specimens of both minerals were identical with carbonate-hydrorylfluorine-apatite. Metabrushite of Julien (1865) and stoffertite of Klein (1901) are identical with brushite. The vague material called epiglaubite by Shepard (1856) is not entitled to further record and probably is identical with brushite. Glaubapatite of Shepard (1856) is a mixture of monetite and apatite.

Zeugite of Julien (1865), pyrophosphorite of Shepard, Jr. (1878), martinite of Kloos (1888), and whitlockite of Frondel (1941), all are identical with artificial β-Ca3(PO4)2. The name whitlockite is reserved for the species. Five localities are now known for this mineral, four in insular phosphate deposits and one in granite pegmatite. The material from three of the insular occurrences is a carbonate-whitlockite, analogous to carbonate-apatite, and has relatively low indices of refraction β-Ca8(PO4)2 definitely forms in nature from water solutions at low temperatures, although all attempts to form the substance artificially have yielded only hydroxyl-apatite. The so-called martinite of Richards (1928) from Ascension Island, south Atlantic, is monetite, and the fourth known occurrence of monetite is noted from Los Monges Islands, West Indies.

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