ZOISITE
Rock&Gem Magazine|December 2020
A Massive Mineral Marked by Christmas- Like Color and Appeal
BOB JONES

It is hard to believe zoisite is a massive mineral that makes lovely Christmas gems, appears in a cartoon, and is also one of the world’s more valuable gems.

I first encountered zoisite in the 1950s when I was already actively attending club meetings and visiting mineral shops. Later, for over two decades, I drove across the country each summer to work on my dad’s farm. Since I was able to stop at countless rock shops during these travels, I became well aware of a remarkable green and red lapidary rock in significant quantities. In those early days, it was described as a recent find from Africa and was immediately popular with lapidary artists and collectors, alike.

DISCOVERING ZOISITE

The massive green mineral was crystalline zoisite, which was slightly sugary looking. Locked in the green stone were hexagonal deep red crystals of ruby, which contrasted with the green host rock. The ruby crystals varied in size and were opaque to translucent in perfect hexagonal form.

The ruby crystal terminations were as much as four inches across. In some of the larger pieces, the exposed termination end of the ruby was slightly translucent, so when domed and polished, the stone showed a lovely chatoyant shimmer. There were no free-standing ruby crystals, but the lovely combination of red ruby and green zoisite in a single rock was attractive to lapidary artists, who soon recognized the red-green combination as an ideal Christmas theme.

A third mineral in the red-green rock was small black spots and crystalline rods, scattered throughout the green zoisite in stark contrast to the red and green colors. In the early days, the black mineral was initially labeled hornblende. Though I did not do lapidary work, I was curious enough to learn about the zoisite-ruby combination.

The discovery of zoisite-ruby rock happened in 1949 when an English prospector named Tom Blevins worked in Tanzania. While prospecting, he came across a deposit of large opaque ruby crystals. He immediately staked claims — in hopes he could make a fortune if some of the rubies proved to be gemmy and could be cut. However, luck was not on his side.

The zoisite deposit was part of a substantial regional metamorphic area composed mainly of schists and marble formations. Mining commenced on the deposit in hopes deeper mining would reveal gem crystals. That did not happen. However, mining of the deposit did prove fruitful — with the discovery of the red-green gemstone combination in 1954. Soon after the discovery, the material was marketed as excellent cutting rough. Before Blevins’ discovery, the local Maasai tribe was aware of the deposit and called it anyoli, which means “green stone.” Even now, you may come across that name on an older specimen of zoisite-ruby rock. Today, some 70 years after its discovery, the Tanganyika’s ruby-zoisite deposit is still the only major source for this lovely carving material. Kenya has produced some but in limited amounts. As time has passed, not only has the name of the country where the zoisite-ruby combination was found changed, so too has the name of the black mineral often found in tandem with the green-red beauty.

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