Carborundum: iridescent silicon carbide, a laboratory material

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Carborundum is silicon carbide made in a factory. Its grey chips with rainbow reflections sold as stones are an industrial material, not a natural mineral.

Key points

Nature	industrial material: silicon carbide (SiC), made by humans
Colour	dark grey to black, with a multicolored iridescent veil
Hardness (Mohs)	about 9 to 9.5 (value given for moissanite, the natural form)
Manufacture	Acheson process, from 1891, in an electric furnace
Origin of the colours	light interference in a thin layer of silica on the surface
Natural form	moissanite, extremely rare (discovered in a meteorite in 1893)
Precautions	sharp chips; do not breathe the dust; wash hands
Traditional correspondences	none ancient; recent associations with the root chakra or the crown, depending on sellers

What is carborundum?

"Carborundum" is the historical name for silicon carbide (SiC), a compound of silicon and carbon. Almost all the silicon carbide in the world is manufactured in factories. It is used as an abrasive (sandpaper, grinding wheels, sharpening stones), as a hard ceramic (brake pads, armor), as a support in furnaces, and as a semiconductor in electronics.

Its large-scale manufacture is credited to the American Edward Goodrich Acheson, in 1891: he was trying to produce artificial diamonds by heating clay and coke, and obtained very hard blue-black crystals that he believed to be a compound of carbon and aluminium, hence the name "carborundum" (formed from "carbon" and "corundum"). He patented the process in 1893 and developed the electric furnace that is still in use.

In its natural form, the same compound is called moissanite. It is extremely rare: the chemist Henri Moissan discovered it in 1893 in the Canyon Diablo meteorite, in Arizona, and the mineral received its name in 1905.

Why is carborundum found among stone sellers?

During industrial grinding or casting, plates of silicon carbide break off and form grey masses with iridescent metallic reflections (blue, violet, gold, pink). These fragments are collected and sold as curiosities under the names "carborundum", "rainbow stone" or "carborundum druzy".

It should be stated plainly: this is not a natural stone, nor a mineral extracted from the earth. It is an industrial by-product. Some sellers present it as a "rare stone" or "meteorite mineral": this is inaccurate. The confusion arises because its natural equivalent, moissanite, does exist in meteorites, but only as tiny grains.

The reflections come from a thin layer of silica (SiO2) that forms on the surface of the silicon carbide: this is light interference, as on a soap bubble.

Traditional symbolism

Carborundum has no ancient tradition. Current associations come from its appearance: dark metal, bright chips, shifting colours. Sellers link it to grounding (the dark colour), to transformation (the changing reflections) and to endurance (its hardness).

These associations are therefore purely recent commercial invention. No study shows any effect on health or well-being. If you like its appearance, keep in mind that it is an aesthetic object and a piece of industrial history.

Traditional correspondences

Area	Correspondence cited
Chakra	root (dark colour) or crown (reflections), depending on sellers
Element	earth or fire (electric furnace)
Signs	no consensus
Keywords	endurance, grounding, change

No ancient source supports these links.

Safety: what to know before handling

Sharp chips: silicon carbide is extremely hard and its fractures have sharp edges. Handle raw pieces with care, especially around children.
Dust: silicon carbide dust is classed as hazardous when inhaled in safety data sheets (hazard statement H350i: may cause cancer by inhalation). Do not sand, grind or file the stone.
No elixirs, not in the mouth.
Hands: wash them after handling pieces that crumble.
Animals: risk of swallowing small fragments.

How to use it

As an object of observation: a rough piece on a stand, under a lamp.
As jewellery: polished pieces are safer than rough ones. Silicon carbide is hard (about 9 to 9.5), so it is not easily scratched, but it is very brittle under impact.
As a curiosity for science lovers: an excellent starting point for talking about abrasives, electricity and meteorites.

Care

Cleaning: a soft dry or barely damp cloth. Water does not harm it, but the reflections come from a fine film that vigorous rubbing can remove.
Products: avoid acids and solvents.
Sunlight: no danger.
Storage: alone, away from soft stones that it could scratch.

Recognising and choosing

An honest seller specifies "silicon carbide", "synthetic material" or "made by humans". Be wary of listings that refer to a meteorite origin, rarity or an "ancient mineral of the Earth". Prices remain modest: if the price is high, it is not justified by the rarity of the material. For a natural stone with iridescent reflections, see hematite or labradorite. For other guidance, read real or fake stone.