Zoisite
Zoisite is a calcium aluminium silicate mineral that occurs in a range of colours, from green, grey and brown to pink, blue and violet. Although the mineral itself is not well known by name, two of its varieties are very familiar to gemstone lovers: tanzanite and ruby in zoisite.
Ruby in zoisite (sometimes called anyolite) is an opaque, bright green zoisite containing crystals of pink to red ruby and often black flecks of hornblende. It comes mainly from Tanzania and Kenya, and its striking red-on-green colouring makes it very popular for beads, cabochons and carvings. Tanzanite is the transparent blue to violet variety, discovered in Tanzania in 1967 and now one of the most popular modern gemstones. Thulite is a pink, opaque variety first found in Norway.
Zoisite was named after Sigmund Zois, a Slovenian naturalist and patron of science who recognised it as a new mineral after a dealer brought him samples from the Saualpe mountains in Austria. It was formally described in 1805.
Zoisite has perfect cleavage in one direction, so it can split if struck hard. Green zoisite and ruby in zoisite are generally untreated, while almost all tanzanite is heat-treated to produce its blue-violet colour.
Zoisite at a glance
| Colour | Green, grey, brown, pink (thulite), blue to violet (tanzanite) |
|---|---|
| Hardness (Mohs scale) | 6 – 7 |
| Composition | Calcium aluminium silicate |
| Crystal structure | Orthorhombic |
| Lustre | Vitreous; pearly on cleavage |
| Transparency | Transparent to opaque |
| Where it is found | Tanzania, Kenya, Norway, Austria, Switzerland, India, Pakistan, Canada and USA |
Caring for zoisite
Zoisite (6 – 7 on the Mohs scale) has perfect cleavage, so protect it from hard knocks and pressure. Clean it with warm soapy water and a soft cloth. Do not use ultrasonic or steam cleaners, and avoid sudden temperature changes and household chemicals. Store it separately from harder stones in a soft pouch.
In folklore
The beliefs below are traditional folklore, included for interest. They are not scientifically proven, and nothing here is medical advice.
Zoisite is a relatively recent discovery, so it does not have the ancient folklore attached to many other stones. Modern tradition regards ruby in zoisite as a stone of the heart and creativity, and tanzanite is a popular gift for a 24th wedding anniversary. Zoisite is associated with the zodiac signs Gemini and Sagittarius.
Zoisite is traditionally believed to help transform negative energy into positive and to encourage the wearer to express their individuality. Ruby in zoisite is associated with joy, passion and vitality, combining the energy of ruby with the growth and renewal linked to green zoisite. Crystal healing lore also holds that zoisite supports recovery after illness or stress. It is linked to the heart chakra.
Related stones
Varieties include ruby in zoisite (anyolite), tanzanite and thulite. Related minerals include epidote and clinozoisite. Stones that can look similar include green aventurine, jade, unakite (granite with pink feldspar and green epidote) and ruby fuchsite, which is sometimes sold as ruby in zoisite but is much softer.
For the technically minded
| Scientific name | Ca2Al3(SiO4)(Si2O7)O(OH) |
|---|---|
| Density | 3.10 – 3.38 |
| Refractive index | 1.696 – 1.718 |
| Double refraction | 0.006 – 0.018 |
| Cleavage | Perfect in one direction |
| Streak | White |
| Fluorescence | Generally none |