A reference on gem minerals, the mines they come from, the people who cut them and the named stones with a documented record.
Gemstones are minerals, and the mineral is the thing that decides most of what follows. A diamond is carbon in a cubic lattice. A ruby and a sapphire are the same mineral, corundum, coloured by chromium in one case and by iron and titanium in the other. Opal is not a crystal at all. The eight sections of this site are organised on that basis — by mineral first, then by the places the material is worked, the stones with an individual record, and the history of how gem material is shaped.
The scale everyone quotes is Friedrich Mohs's, published in 1812. It ranks ten reference minerals in the order they scratch one another and it measures nothing else: not toughness, not cleavage resistance, not hardness in the engineering sense. It is a useful example of how much of this subject is a matter of what a number actually claims.
How the pages are organised
Five sections cover mineral families — corundum, beryl, quartz, diamond, and the drawer of everything with no major family of its own. Three cover the work: the named mines and trade centres, the individual stones with a documented provenance, and the cutting traditions from the rose cut to Tolkowsky's 1919 proportions. Every carat weight, date and dimension is attributed in the sentence that carries it, to the museum catalogue, laboratory report or mine operator's record it came from.
The complete list of pages is on the archive.