Sphalerite

Sphalerite, also known as Blende, is one of the few minerals having six directions of cleavage. If six directions are perfectly cleaved on a single crystal, it forms rhombic dodecahedron. However, identifying the six directions in a single piece is quite difficult because of multiple twinning and the many directions. Only the abundant cleavage at different directions are seen easily.

The name sphalerite has been derived from Greek word for treacherous rock and Blend from German for blind or deceiving. The black and red crystal forms of sphalerite are also nick named as Black Jack and Ruby Jack. The iron content in it increases the darker shade and opaque metallic crystals are known as Marmatite. Sphalerite is sometimes difficult to identify from valuable minerals like galena, acanthite and tetrahedrite.

Notable occurrences of sphalerite are Tri state area near Joplin, Missouri; Rosiclare, Illinos; Elmwood, Tennessee, USA and Broken Hill, Australia. It is also found in Italy, Spain, Burma, Peru, Morocco, Germany and England. The hardness of the stone is 3.5 - 4 and specific gravity is 4, heavier than average, but if compared to most metallic minerals, it is light.

Techinical Specification

Name	Moh's	Specific Gravity	Structure	Cleavage	Refractive Index	Double	Disp.	Pleochro	Fluorescence
Sphalerite	3.5+	4.08-4.10	Cubic	Perfect	2.368-2.371	None	0.156	None	Variable to None