Rare Gem Cobaltocalcite

 

Rare Cobaltocalcite from Spain
Rare Cobaltocalcite from Spain

Some time ago we acquired some unusual specimens from the estate of a collector who had travelled the world acquiring rare minerals. Among them were some large gemmy crystals in a vivid reddish purple that we had never seen before. The material was labelled as originating from Spain.

We faceted several pieces and were delighted with the color saturation and translucency. The cut stones displayed a wonderful glow when backlit. But we noticed the material was fairly soft. So we suspected it might be a form of calcite, a mineral treasured by collectors for its fascinating diversity. Though it is not a good jewelry stone due to its softness (3 on the Mohs scale), calcite occurs in a variety of crystal forms and in a huge range of colors. Nearly every calcite is unique.

We took a 16.78 ct polished gem to GIA in Bangkok for testing and they confirmed it was cobaltocalcite, a rare calcite colored by trace amounts of cobalt.

Cobaltocalcite Rough and Polished
Cobaltocalcite Rough and Polished

In addition to their usual report, GIA issued a special letter that testifies to the rarity of this particular material. Here is an excerpt:

"Gem quality cobaltocalcite may be recovered from many sources around the world, but the vast majority of material from all these sources usually produces an aggregrate of small closely packed crystals on a rock matrix or larger single crystals of lower quality. Rough crystals that will cut large fine stones are occasionally found but are in the minority. Very fine, large gem-quality cobaltocalcite of over 10 carats with good transparency and distinctive saturated color can be considered extremely scarce. The large size, highly saturated reddish purple color and high degree of transparency makes this a notable cobaltocalcite."

GIA was so intrigued by this material that they requested samples of the rough material to do additional analysis in their lab. They wrote up their findings in the Spring 2015 issue of their journal, Gems & Gemology. They discovered that the unusually vivid color of our cobaltocalcite was due to high concentrations of cobalt with possible contribution from traces of manganese.

Rare Cobaltocalcite

We now are pleased to offer a small number of these world-class gems to collectors. 

See our collection of Rare Faceted Cobaltocalcite

 
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