Naturally perfect cubes, mostly from Navajún in Spain. The best are near-flawless.
Spain, Peru, Italy, and almost every sulphide deposit on earth3 references
For your own specimen, Stone Identifier AI Rock Scan — Lovenhall’s rock, crystal & mineral identifier app, free to try on iPhone & iPad — names the rock, mineral or crystal from a photo, with its hardness and rarity.
The cubes people photograph and disbelieve come almost entirely from one mine at Navajún in La Rioja, Spain, where pyrite grew in a soft marl that let the crystals develop unimpeded faces. The result is cubes so geometrically clean that the usual first reaction is that they must be man-made.
They are not, and there is a way to tell. Natural Navajún cubes carry very fine parallel striations on their faces, and the striations run at right angles between adjacent faces — a growth feature of the cubic system that no polishing produces. They also sit in or on a pale grey-brown matrix, often with the impression of the crystal still in the rock, and the faces have minute growth steps rather than a uniform polish.
Cultured pyrite exists and is sold legitimately. It tends to come as loose cubes with no matrix, in matched sizes, with faces that are flat and bright but striation-free. Neither is a fake; the difference is what you are paying for.
Navajún, La Rioja (Spain) · Pyritohedron · Interpenetrant twins
Establish which of these you are holding before judging it. A genuine piece read against another reference's rules will look wrong when it is not.
These apply to this model and not to the rest of Pyrite. Work them alongside the maker's general checks, not instead of them.
Under good light and a loupe, each face of a natural cube shows fine parallel lines, and the direction rotates ninety degrees on the neighbouring face. This is a growth signature of cubic pyrite and it is the clearest mark of natural origin.
Natural cubes come out of rock and usually keep some. Look for a matrix whose cavity matches the crystal, with the impression of the faces preserved. A cube glued into an unrelated rock leaves a visible adhesive line at the join.
A tray of cubes all within a millimetre of each other in size, all equally bright and none on matrix, is a cultured product. Natural material from one pocket varies.
A single sharp Spanish cube on matrix runs $20 – 200 by size and perfection; exceptional plates reach four figures.
An orientation for honest, unrestored condition — never an appraisal, and never a quotation.
Lovenhall StoneThe tests tell you what it is. The instrument reads a photograph and offers a name to start from — then hands you back to the tile and the coin, which are what settle it.