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FLUOR-SPAR. 223 9. Tetrahedron, truncated on the edges. The crystals are large, middle-sized, small, and very small, and are placed on one another, or side by side. The surface is smooth and splendent, or drusy and rough. Internally the lustre is specular-splendent, or shining, and is vitreous, inclining to pearly, and sometimes to adamantine. The fracture is cither perfect or imperfect foliated, with a fourfold equiangular cleavage, which is parallel with the planes of an octahedron or tetrahedron. The fragments are octahedral or tetrahedral. It occurs in distinct concretions, which are sometimes large, coarse, and small granular, sometimes thick and curved lamellar, and occasionally columnar, which latter sometimes exhibits fortification-wise curved violet stripes. It alternates from translucent to transparent, and re fracts single. It is semi-hard ; harder than cakareous-spar. It is brittle. It is very easily frangible. Specific gravity, 3.09-13,—3.1911, Ilaug. 3.148, Gel- lert. 3092, Jirisson. 3. loti,—3.184, Muschcnbrucck. 3.138, 3.228, Karstcn. Chemical Characters. Before the blowpipe, it generally decrepitates, gra dually loses its colour and transparency, and melts, with- 0ll t addition, into a greyish-white glass. When two fragments are rubbed against each other, they become luminous in the dark. When gently heated, oi laid on glowing coal, it phosphoresces, (particularly the sky-blue, violet-blue, and green varieties,) partly with a blue, part- ty with a green light. When brought to a red-heat, it