黑柱石
CaFe2+2Fe3+(Si2O7)O(OH)
Ilvaite is a sorosilicate mineral recognized among collectors for its crystal form and distribution, with known Chinese sources.
Ilvaite is a calcium iron sorosilicate that forms in iron skarns and metasomatic deposits. Its opaque black crystals — with a near-metallic to resinous lustre and a sharp, deeply striated prismatic habit — have made it one of the most sought-after skarn minerals, and China is now its definitive source.
The Huanggang standard
Since the 2000s the Huanggang iron-tin skarn in Hexigten Banner, Inner Mongolia, has produced jet-black, lustrous, deeply striated ilvaite prisms to 10 cm and beyond, frequently perched on contrasting quartz, calcite, or fluorite and associated with green hedenbergite and andradite garnet. This material drew renewed collector attention to the species.
What collectors look for
Crystal sharpness, length, and the silvery-black lustre that catches the light along the striations are the value drivers, together with an undamaged termination and an aesthetic association — hedenbergite sprays, druzy quartz, or fluorite. Combination pieces are especially prized.
Care
Ilvaite is stable but, like many iron-rich species, is best kept dry and out of prolonged strong light; avoid acids when cleaning. See the Huanggang Mine page for the locality in detail.
