We currently have 2 in stock.
Obsidian is a natural volcanic glass formed by the rapid cooling of viscous lava. It is a unique and fascinating rock found in various locations around the world, including New Zealand.
WARNING: Take care with handling as the edges can be very sharp!
Igneous: Rock formed from rapidly cooled lava flows (therefore technically a 'volcanic igneous' rock).
Found: Mayor Island (Tuhua) in the Bay of Plenty, and parts of Northland, New Zealand. (Note, the rocks for sale are not sourced from New Zealand but are technically very similar to those found here.)
Sizes: Shelf specimens (about 300–800g).
Note: Images are examples of specimens only. Sizes and shapes will vary.
More detail
Structure
Obsidian is an amorphous, non-crystalline rock with a glassy structure. It is primarily composed of silicon dioxide, typically containing 70-75% silica content, with additional elements like iron, magnesium, and calcium.
Type
Volcanic igneous.
Physical properties of obsidian
Colour: Typically black, but can also appear in brown, grey, red, or even green.
Lustre: Glassy or vitreous lustre, reflecting light and creating a smooth, shiny appearance.
Hardness: Ranges from 5 to 5.5 on the Mohs scale, making it softer than quartz but harder than many common metals.
Density: Approximately 2.55 grams per cubic centimetre.
Fracture: Exhibits a conchoidal fracture, breaking with smooth, curved surfaces resembling the interior of a seashell. Ideal for knapping into pointed weapons and cutting tools.
General Properties of obsidian
Glass-like texture: Has a smooth, glass-like texture due to its rapid cooling, which prevents crystal formation.
Low water content: Typically contains less than 1% water by weight.
Brittleness: While hard, obsidian is also brittle and easily breaks with sharp edges.
Translucency: Some varieties can be translucent when thin slices are held up to the light.
Chemical composition: Primarily composed of silica with smaller amounts of other elements like aluminum, iron, magnesium, sodium, and potassium.
Uses of obsidian in New Zealand and worldwide
Early Māori: Obsidian was highly prized by the Māori and used for various purposes, including cutting tools and weapons.
Prehistoric tools: Used for making sharp cutting tools, arrowheads, and blades due to its ability to form extremely sharp edges.
Modern surgical instruments: Some modern surgical scalpels use obsidian blades, which can be sharper than steel.
Jewellery and decorative objects: Used in jewellery making and decorative items due to its attractive appearance.
Archaeological studies: Studied by archaeologists to trace ancient trade routes and understand prehistoric cultures.
Geological research: Analysed by geologists to understand volcanic processes and lava compositions.
Ornamental stone: Used as an ornamental stone in various applications due to its unique appearance.
Cultural significance: Holds cultural and spiritual significance in various societies, including Māori culture in New Zealand.