One composition, many appearances. Amethyst is a purple variety of quartz; chalcedony is a microcrystalline form. They are not separate mineral species in this index.
Reference photograph of clear quartz. Specimen origin is not documented by the image source; this is not a Sidi Rahal specimen. W.carter · CC BY-SA 4.0. Image unchanged.SiO₂
Mineral family
Silica
Crystal system
Trigonal (α-quartz)
Mohs hardness
7
Colour
Colourless; many coloured varieties
Typical appearance
Often prisms with pointed terminations; also microcrystalline.
