Dolomite: Gemstones Information
Dolomite is CaMg(CO3)2 and forms transparent colourless to light yellow rhombohedral crystals of the trigonal system. The hardness is 3.5–4 and there is one direction of perfect cleavage. Faces may sometimes be curved. The SG is 2.8–2.9, and the RI 1.502 and 1.681 with birefringence of 0.179, uniaxial negative. Dolomite occurs in a number of conditions: in sedimentary rocks, in altered Mg-rich igneous rocks or in geodes.Perhaps the finest transparent dolomite crystals are those found at Eugui, Navarra Province, Spain. Massive dolomite or ‘dolomitic marble’ is often banded and in colours of red, brown, yellow, green and white.Such material comes from the US and Brazil.