_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.