Mtorolite

(via Wahroongai News, Vol 30, No.4, April, 1996) Grahame Brown writes:

Mtorolite is a rare green chrome chalcedony that occurs in one location in the world: Zimbabwe. Here it occurs as horizontally pitched veins that intrude decomposed serpentine bordering the Great Dyke. Although commercially mined out, it is considered that significant reserves remain to challenge the diligent fossicker. Better quality mtorolite can be faceted; but mostly this attractive chrome chalcedony is cabochoned or carved.

According to Ian Campbel (pp 19-23) in the October 95 issue of The South African Gemmologist, mtorolite was named for the Mtoroshanga of Zimbabwe, the district that hosts the only known occurrence of this gem material in the world. The greenish hues possible in this chalcedony depend on its Cr:Ni content, while the saturation of its green color depends of its Cr content. For example, dark green good quality evenly colored mtorolite has 0.04% Cr and 0.02% Ni, while pale green variegated mtorolite has 0.205 Cr and <0.01% Ni.

Mtorolite has colors that vary from a saturated chrome green to pale grayish green hue; a specific gravity of 2.57 – 2.60; a spot RI of 1.54. It has a pinkish to reddish Chelsea Filter reaction and is inert to both LW and SW UV.