silicates
Garnet
- Also known as
- carbuncle
- Crystal system
- cubic
- Hardness
- 6.5–7.5 on the Mohs scale
- Lustre
- vitreous
- Colour
- Red most familiarly, but also orange, green, yellow, purple and colourless
- Where it forms
- Chiefly in metamorphic rocks, and it is one of the most useful minerals in geology for exactly that reason — the composition of a garnet records the pressure and temperature it grew at, so a garnet is a thermometer and a barometer for a rock’s history.
- Chiefly from
- worldwideIndiaMadagascarTanzaniaRussia
Why it is that colour
Depends entirely on which garnet it is. Iron gives the deep reds of almandine, magnesium the lighter reds of pyrope, manganese the orange of spessartine, chromium the green of uvarovite and tsavorite.
Safety
Safe to handle. Garnet is used as an industrial abrasive, and cutting it produces dust which should not be inhaled, as with any mineral dust.
Where it comes from
Abundant. India is the largest producer of industrial garnet, used in waterjet cutting and sandblasting, and gem material is a minor by-product of a bulk mineral trade. Tanzanian and Kenyan tsavorite mining is small-scale and less regulated.
Historical use
Anglo-Saxon and Merovingian goldsmiths set thin slices of garnet over patterned gold foil in cloisonné work — the Sutton Hoo shoulder clasps are the famous example — and recent analysis has traced that garnet to India and Sri Lanka, evidencing trade routes across the whole of Eurasia in the seventh century.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
Red garnet, usually called carbuncle in older sources, is documented from Bronze Age Egypt onward and appears throughout classical and medieval writing, generally as a stone of blood, vitality and protection for travellers. That reading is genuinely old. What is modern is the assignment of different meanings to different garnet species, since the species were not distinguished until the nineteenth century.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Worth knowing
Garnet is not a mineral. It is a group of at least fifteen approved species sharing one structure, in which two positions in the lattice can be occupied by different metals — and every intermediate composition exists, so most natural garnets are mixtures of several end members rather than any one of them.
That is why a garnet is such a good geological instrument. Which metals a garnet took up, and in what proportion, depends on the pressure, the temperature and the chemistry of the rock as it grew. Garnets often grow in zones, recording changing conditions from core to rim, so a single crystal can preserve the pressure-temperature path of a mountain range being built.
The Sutton Hoo garnets are a small marvel of archaeology. Thousands of individually cut slivers, each backed with hatched gold foil to throw light back through the stone, and the raw material carried from South Asia to East Anglia in the seventh century.
Identity checked against IMA-CNMNC master list, June 2025.