Amethyst, citrine, and rose quartz are names people use for color. The mineral species is quartz. The formula is silicon dioxide, SiO2. This page keeps the host and the variety names on one species card, then points to the public pages that list them that way.
The host is SiO2
The Handbook of Mineralogy quartz PDF names the species quartz, formula SiO2, crystal data hexagonal, hardness 7, conchoidal fracture. Webmineral records the same formula, trigonal crystal system, hardness 7, and a synonym list of color and texture names, not separate species. USGS silica statistics sit on the commodity side: industrial sand, high-purity quartz, and cultured quartz crystal. None of those pages sell a specimen, and this hub does not invent a locality price.
A six-sided prism with a pyramidal tip is the usual crystal habit. Massive chunks without faces are still quartz. Color does not change the formula.
Varieties, not species
Webmineral’s quartz page lists, among others:
- Amethyst: purple
- Citrine: yellow
- Rose quartz: rose colored
- Rock crystal, smoky quartz, and several microcrystalline names (chalcedony, agate, flint) that this hub does not card separately
Those are variety names on the quartz species. They are not IMA species of their own. Cards under Amethyst, Citrine, and Rose quartz cite the quartz PDF and the Webmineral quartz page for that reason.
| Shop name | What the species page says | Kind card |
|---|---|---|
| Clear quartz / rock crystal | Quartz, SiO2, often colorless to white | Quartz |
| Amethyst | Purple variety of quartz | Amethyst |
| Citrine | Yellow variety of quartz; most market material is heated amethyst (GIA) | Citrine |
| Rose quartz | Rose-colored quartz, often massive rather than sharp points | Rose quartz |
Worked example: a yellow cluster labeled citrine
On the table. Hexagonal points in a druse. Hardness 7. Golden to orange color, often strongest at the tips.
Species. Quartz (SiO2). Handbook of Mineralogy + Webmineral. Color is allowed on that species page; yellow is one of the listed colors.
Variety vs treatment. GIA’s citrine FAQ: yellow quartz colors are rare in nature; most citrine is the result of heating, which converts purple amethyst to golden shades. Heated amethyst is still quartz. The trade name “citrine” does not make a new mineral.
Uses. Jewelry, collecting, and display of the same SiO2 host.
Worked example: purple points vs a purple cube
Purple is not a species. A six-sided purple prism at hardness 7 is amethyst, quartz. A purple cube at hardness 4 with {111} cleavage is fluorite. CaF2. The identify guide walks that split: How to identify a mineral specimen.
Start on Quartz when the habit and hardness match SiO2. Use the variety cards for the color names. Open the species PDF before a shop label. A jeweler loupe and a Mohs kit are the table tools for that check, not a display stand: ID kit vs display stand.
Sources
- Handbook of Mineralogy, Mineralogical Society of America. Quartz (SiO2) species PDF: https://www.handbookofmineralogy.org/pdfs/quartz.pdf
- Webmineral. Quartz mineral data (formula, hardness 7, synonym list: amethyst, citrine, rose quartz): https://webmineral.com/data/Quartz.shtml
- U.S. Geological Survey, National Minerals Information Center. Silica statistics and information: https://www.usgs.gov/centers/national-minerals-information-center/silica-statistics-and-information
- Gemological Institute of America. “Is citrine treated?”: https://www.gia.edu/gia-faq-treated-citrine
Updated 2026-08-31.