Celestite geodes have been found in parts of Coke, Fisher, and Nolan counties, but these geodes contain little gem material. Diamond _Composition_: carbon. _Crystal system_: isometric. _Hardness_: 10. _Specific gravity_: 3.51 to 3.53. _Luster_: adamantine to greasy. _Color_: brown, colorless, pink, blue, yellow, and various other light colors; rarely deeply colored; sometimes black. _Cleavage_: four directions, octahedral, perfect. _Fracture_: conchoidal. _Tenacity_: brittle. _Diaphaneity_: transparent to opaque. _Refractive index_: 2.42. _Dispersion_: high. There is only one well-authenticated find of diamond in Texas. A small brownish diamond was found in 1911 on section 64, block 44, Foard County (Sterrett, 1912, pp. 1040-1041). The exact weight of the stone has not been recorded, but one authority estimated that it was of sufficient size and clarity to yield a cut stone of about one-quarter carat. The only diamond-bearing rocks known in the United States are in Pike County, Arkansas. Although many other diamonds have been found in the United States, all were loose in gravels or streams except for some stones at the Arkansas locality. The fact that one diamond was found in Foard County does not mean that the prospects of finding more diamonds in Texas are much better there than anywhere else in the State. It is highly unlikely that more than a very few diamonds will ever be found in Texas, and any stones that may be found in the future are likely to be widely scattered. Epidote _Composition_: HCa₂(Al, Fe)₂Si₃O₁₃. _Crystal system_: monoclinic. _Hardness_: 6 to 7. _Specific gravity_: 3.25 to 3.5. _Luster_: vitreous. _Color_: yellowish green to brownish green and brown. _Streak_: uncolored to grayish. _Cleavage_: two directions. _Fracture_: uneven. _Tenacity_: brittle. _Diaphaneity_: transparent to opaque. _Refractive index_: about 1.72 to 1.77. Llano County has furnished some green and brownish-green epidote that is suitable for cutting into cabochons. Most of the material that approaches gem quality has come from contact metamorphic zones and is associated with garnet, quartz, and some scheelite. Some small cavities in the rocks contain tiny transparent crystals of gem quality, but the largest obtainable flawless faceted stones would probably be less than 15 points. Faceted stones of epidote are sometimes known as pistacite owing to their common pistachio-green color. Fluorite _Composition_: CaF₂. _Crystal system_: isometric. _Hardness_: 4. _Specific gravity_: 3.0 to 3.25. _Luster_: vitreous. _Color_: violet, blue, colorless, green, yellow, brown, rose, and crimson red. _Streak_: white. _Cleavage_: four directions, octahedral, perfect. _Fracture_: subconchoidal to splintery. _Tenacity_: brittle. _Diaphaneity_: transparent to subtranslucent. _Refractive index_: 1.434.