Zoisita Tanzanita
Zoisita is a mineral with formula Ca₂Al₃(SiO₄)(Si₂O₇)O(OH), in the Silicato [Sorosilicato (Grupo Epidota)] group. This specimen comes from Merelani Hills, Lelatema Mountains, Simanjiro District, Manyara, Tanzania and joined the Terrium collection in 2025.
Description
Metallic cubic crystals of lead-grey colour on a thumbnail-sized matrix of compact white calcite.
History of this specimen
It came into my collection after a small incident that reinforced my trust in Spirifer Minerals. On a previous purchase a native silver went missing, and without any quibble they refunded me. With that amount, a small top-up and a discount, I ended up buying this tanzanite. Since then I associate it with something as simple—and as important—as doing things properly.
About Zoisita
Tanzanite is a vanadium-rich zoisite, a calcium–aluminium sorosilicate of the epidote group, with ideal formula Ca₂Al₃(Si₂O₇)(SiO₄)O(OH), in which V³⁺ partially substitutes for Al³⁺ as the chromophore. Zoisite is a relatively common mineral in calcium-rich metamorphic rocks—schists, gneisses, amphibolites and metamorphosed marbles—and is the orthorhombic polymorph of clinozoisite, which crystallises in the monoclinic system. Tanzanite is its blue-violet gem variety, discovered in 1967 at Merelani, and shows strong pleochroism: colour ranges from deep blue to violet and grey–lavender tones depending on crystallographic orientation. Virtually all commercial production is subjected to controlled heating, around 500–600 °C, which modifies colour centres and removes brownish or greenish hues, stabilising the purer blue.
About the locality
Merelani Hills is the only tanzanite locality worldwide, with continuous production since 1967, and lies not far from Kilimanjaro. It yields well-defined prismatic crystals with intense pleochroism, and a production volume with no global equivalent. It is an area traditionally inhabited by Maasai communities and other local groups, where mining has overlaid traditional agro-pastoral economies. The state framework is relatively stable, though with economic imbalances and harsh conditions typical of artisanal mining. Working in the mine is not an adventure.
Technical data
- Catalogue No.
- 0301
- Composition
- Ca₂Al₃(SiO₄)(Si₂O₇)O(OH)
- Name
- Zoisita
- Variety
- Tanzanita
- Group
- Silicato [Sorosilicato (Grupo Epidota)]
- Category
- Estélites
- Mine
- Merelani Hills
- District / Municipality
- Lelatema Mountains
- Province
- Simanjiro District
- Region
- Manyara
- Country
- Tanzania
- Size (cm)
- 2.8 x 1 x 1
- Weight
- 6.4 g
- Acquired
- 2025
- Etymology
- “Zoisite” honours Baron Sigmund Zois (1747–1819), a patron of Central European mineralogy. “Tanzanite” is the trade name coined by Tiffany & Co. in 1967 in reference to Tanzania.
- Quality
- Top
- Value trend
- Al alza
Related specimens
- Epidota — Austria
- Gummita (Pseudomorfo de Uraninita) — Tanzania