Quartz
Clear rock crystal, or stones kept for what grew inside them — rutile needles, chlorite, a landscape in a window.
Hardness — 7 Care — everyday; avoid thermal shock Source — Brazil, Arkansas, the Alps
Quartz
Crystalline quartz, hardness seven — the working definition of an everyday stone. The coloured varieties fade with long sunlight, so they go back in the box rather than living on a windowsill.
Amethyst
Quartz coloured by iron. Hard enough for daily wear but it will fade in prolonged direct sun, so it goes back in its box rather than sitting on a windowsill.
Hardness — 7 Care — avoid prolonged sunlight Source — Brazil, Uruguay
Citrine
Yellow to amber quartz. Most on the market is heated amethyst; natural citrine is scarcer and paler, and I say which a stone is when I know.
Hardness — 7 Care — avoid prolonged sunlight Source — Brazil, Zambia