Mineral · Al2SiO5 polymorphs
Andalusite
Al2(SiO4)O
Andalusite is the low-pressure Al2SiO5 polymorph forming square prisms in contact-metamorphosed shales; chiastolite is the variety with a black cross of graphite inclusions in cross-section, from Lancaster (Massachusetts), Spain and Australia. Polished chiastolite slices are the collector's item. Gem andalusite from Brazil is strongly pleochroic.
| Formula | Al2(SiO4)O |
|---|---|
| IMA status | grandfathered |
| Crystal system | Orthorhombic |
| Mohs hardness | 6.5–7.5 |
| Group | Al2SiO5 polymorphs |
| Type locality | Andalusia, Spain (historical) |
| Streak | White |
| Specific gravity | 3.15 |
| Reference list | IMA List of Minerals (RRUFF) — verify formula and status against the current list |
Elsewhere
Cite this article
Stratum Study. "Andalusite" (Mineral). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/minerals/andalusite. Accessed 2026-09-20.
@misc{stratum-andalusite,
title = {Andalusite},
author = {{Stratum Study}},
howpublished = {\url{https://stratum.black/study/minerals/andalusite}},
year = {2026},
note = {Mineral article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, wikidata, commons. Accessed 2026-09-20.}
} Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.