Obsidian
Obsidian is a natural volcanic glass formed when lava rich in silica cools so quickly that crystals do not have time to grow. Because it is a glass rather than a mineral, it has no crystal structure, and it breaks with smooth, curved (conchoidal) fractures that can produce edges sharper than a steel blade. It is usually black, but can also be brown, grey, green or red, and is often banded or spotted.
Many varieties are popular for beads and carvings. Snowflake obsidian has white, flower-like patches of cristobalite crystals. Mahogany obsidian is mottled black and reddish-brown, coloured by iron. Gold and silver sheen obsidian contain tiny aligned gas bubbles that create a metallic sheen, while rainbow obsidian shows bands of iridescent colour caused by tiny mineral inclusions. Apache tears are small, rounded nodules of obsidian that look translucent when held up to light.
Obsidian has been used since the Stone Age to make knives, arrowheads and scrapers, and it was traded over long distances; its source can often be traced from its chemistry. The Aztecs and other Mesoamerican peoples used it for blades and polished it into mirrors used for divination. The 16th-century English scholar John Dee owned an Aztec obsidian mirror, which is now in the British Museum. Obsidian blades are still sometimes used in specialist surgery because of their sharpness.
Obsidian is found wherever there has been recent volcanic activity, including Mexico, the USA, Armenia, Iceland, Italy, Turkey, Japan and New Zealand. Black glass is sometimes sold as obsidian, and "green obsidian" or "blue obsidian" beads are usually man-made glass.
Obsidian at a glance
| Colour | Black, brown, grey, green, red; snowflake, mahogany, sheen, rainbow |
|---|---|
| Hardness (Mohs scale) | 5 – 5.5 |
| Composition | Volcanic glass, mainly silica with aluminium, iron, potassium, sodium |
| Crystal structure | Amorphous (natural glass) |
| Lustre | Vitreous |
| Transparency | Translucent to opaque |
| Where it is found | Mexico, USA, Armenia, Iceland, Italy, Turkey, Japan, New Zealand, Ethiopia and Peru |
Caring for obsidian
Obsidian is relatively soft (5 – 5.5 on the Mohs scale) and brittle, so it can scratch, chip or break if dropped or knocked. Clean it with warm soapy water and a soft cloth, then dry. Avoid ultrasonic and steam cleaners, harsh chemicals and sudden temperature changes. Store separately from harder stones in a soft pouch. Broken obsidian edges can be extremely sharp.
In folklore
The beliefs below are traditional folklore, included for interest. They are not scientifically proven, and nothing here is medical advice.
In Mesoamerica, obsidian was sacred to the Aztec god Tezcatlipoca, whose name means "smoking mirror", and polished obsidian mirrors were used to see into the future and the spirit world. Legend tells that Apache tears are the tears of Apache women mourning warriors who died rather than be captured, and that whoever carries one will never cry again. Obsidian is associated with the zodiac sign Scorpio and Sagittarius.
Obsidian is traditionally regarded as a powerful protective and grounding stone. Crystal healing lore holds that it shields the wearer from negativity, helps reveal hidden truths and supports emotional healing by bringing buried feelings to the surface. Snowflake obsidian is associated with balance and calm, and Apache tears with comfort in grief. It is linked to the root chakra.
Related stones
Snowflake obsidian, mahogany obsidian, gold sheen obsidian, silver sheen obsidian, rainbow obsidian, Apache tears and fire obsidian. Other natural glasses include moldavite, Libyan desert glass and tektites. Stones that can look similar include black onyx, jet, black tourmaline, hematite and black glass.
For the technically minded
| Scientific name | SiO2 (+ oxides; volcanic glass) |
|---|---|
| Density | 2.33 – 2.60 |
| Refractive index | 1.48 – 1.51 |
| Double refraction | None (amorphous) |
| Cleavage | None |
| Streak | White |
| Fluorescence | None |