Correspondence tables

Correspondence tables are cultural documents. They record what practitioners in a particular period associated with a particular material, and they change — sometimes sharply — from one generation of published sources to the next. Treated as such, they are genuinely useful: they tell you how a stone has been used, by whom, and since roughly when. Treated as mineral properties, they mislead, and they make it impossible to tell a well-attested traditional use from a table invented in the 1980s.

Every entry below therefore keeps two registers apart. The identification data — hardness, crystal system, habit, colour cause — is checkable against standard handbooks, and the entry names them. The correspondences follow, with the earliest source we can point to. Where a common attribution has no traceable source older than the late twentieth century, the entry says so plainly rather than quietly omitting the date.