Polished Obsidian Sphere

Obsidian is volcanic glass, formed when lava cools too fast to crystallise, and polished to a sphere it produces one of the deepest blacks available in a natural material. The surface goes to a genuine mirror finish, so the piece picks up a compressed reflection of whatever is around it and reads as much darker than the room it sits in. On a pale table it becomes the thing your eye returns to.

Two sizes are offered. The three centimetre sphere is a desk object, small enough to sit in a dish with other found things or hold while you think. The ten centimetre sphere is a proper centrepiece for a coffee table, a console or a low shelf, heavy enough that it needs a stable flat surface. Each stone is natural, so subtle banding, sheen and inclusions vary from piece to piece and no two are identical.

This is sold purely as a decorative object. No properties of any kind are claimed for it beyond how it looks. Handle it as you would any polished glass: it is hard but brittle, and a fall onto a hard floor will chip the surface. Wipe with a soft dry cloth to keep the polish clean, and avoid abrasive pads and household cleaning sprays.

• Natural polished obsidian, a volcanic glass
• Available in 3 cm and 10 cm diameters
• Deep mirror-polished black finish
• Banding and sheen vary piece to piece
• Place on a stable flat surface
• Wipe with a soft dry cloth
• Brittle: avoid knocks and hard floors
• Decorative only, no properties claimed