Twin plane _a_ (100). Birefringence moderate, positive; plane of optic axes perpendicular to _b_, nearly parallel to _a_. Acute bisectrix inclined to _c_ at angle of 1°-4°. Dispersion feeble, ρ < υ. Brittle. Hardness 5-5¹⁄₂; sp. gr. 4·9-5·3; conchoidal fracture. Lustre resinous. Colour, red to brown, yellow, yellowish- and greenish-brown. Transparent when pure; more often translucent to opaque. Monazite is with difficulty soluble in acids; before the blowpipe it is infusible; when moistened with sulphuric acid it colours the flame greenish-blue. The mineral often occurs massive, yielding angular fragments, but is most common in rolled grains. It occurs in the gneiss of the Carolinas and Georgia, and in sands derived from the gneiss, in Idaho and many of the Pacific States; in Brazil, at various localities in the provinces of Minas Geraes, Bahia, Espirito Santo; in Queensland, Australia; in Madagascar; in Ceylon; near Travancore in India; in the Urals; in Scandinavia, etc. The deposits of commercial value will be treated more fully in the next chapter. It is of wide distribution as an accessory constituent of granites, diorites, and gneisses. Monazite was first described, under the name Turnerite, by Lévy,[103] in 1823; the specimen was from the collection of the English chemist Turner, who thought it a variety of sphene (titanite), and was named after him at the suggestion of the mineralogist Heuland. The specimen was stated to have been found in Dauphiné, but in spite of considerable examination of the question, the precise locality is still unknown. The resemblance between Turnerite and the mineral later described as monazite (μοναζειν = to be solitary) was pointed out by Dana in 1866, and confirmed by Pisani, 1877. The name Monazite was first used by Breithaupt[104] in describing a mineral found by Menge (1826) accompanying zircon in a granite from Miask in the Urals. Breithaupt concluded, from the high specific gravity, that the mineral contained a heavy metallic oxide. It was again described as Mengite by Brooke[105] in 1831. It was re-discovered by Shephard[106] in South Carolina in 1837, and described by him under the name Edwardsite, a variety from Connecticut being called Eremite. To Shephard belongs the honour of having discovered its true nature; after analysis he described it as a ‘Basic Sesquiphosphate of the Protoxide of Cerium,’ giving the formula (modern notation) 3CeO,2P₂O₅, and finding also zirconia, alumina, and silica in it (his specimen was probably very impure). Gustav Rose[107] showed this to be identical with monazite in 1840. In 1846 Wöhler described, under the name Cryptolite, a variety of tetragonal habit closely resembling zircon. This occurs at Arendal in Norway, enclosed by apatite, in the granite; it may be obtained by treatment with dilute nitric acid, which dissolves the apatite. [103] _Annals of Philosophy_, 1823, ~21~, 241. [104] _Schweigg. J._ 1829, ~55~, 30.