Physical Properties of Diamonds :  Diamonds are very hard and their color is variable and tends toward pale yellows, browns, grays, and also white, blue, black, reddish, greenish and colorless. Luster is adamantine to waxy. Transparency crystals are transparent to translucent in rough crystals. Crystal System is isometric Crystal Habits include isometric forms such as cubes and octahedrons, twinning is also seen. Hardness is 10 Specific Gravity is 3.5 (above average) Cleavage is perfect in 4 directions forming octahedrons. Fracture is conchoidal. Streak is white. Associated Minerals are limited to those found in kimberlite rock, an ultramafic igneous rock composed mostly of olivine. Other Characteristics: refractive index is 2.4 ( very high), dispersion is 0.044, fluorescent. Notable Occurrences include South Africa and other localities throughout Africa, Australia, Brazil, India Russia,  and Arkansas. The best indicator of Diamonds is its Extreme hardness.