Holmquistite is a lithium magnesium aluminum inosilicate mineral with chemical formula: Li2(Mg, Fe2+)3Al2Si8O22(OH)2. It is a mineral consisting of an alkali and a silicate of iron, magnesium, lithium, and aluminum and related to hornblende. It is a rare mineral that occurs as a metasomatic replacement near that outside of lithium-rich pegmatites. Color could vary from black, dark violet to light sky blue.
It was first described in 1913 from an occurrence in Utö, near Stockholm, Sweden. It was named for the Swedish petrologist Per Johan Holmquist (1866–1946).
- Category: Inosilicate
- Formula: Li2(Mg,Fe2+)3Al2Si8O22(OH)2.
- Crystal system: Orthorhombic
- Member of: Holmquistite Root Name Group
Fig: Holmquistite – lithium magnesium aluminum inosilicate mineral
Holmquistite forms prismatic or acicular crystals up to 10 cm or as columnar sheaflike, massive aggregates. The color varies from black, dark violet to light sky-blue. It crystallizes in the orthorhombic crystal system as prismatic crystals up to 10 cm (3.9 in) or as massive aggregates. It has a Mohs hardness of 5-6 and a specific gravity of 2.95 to 3.13.
- Cleavage: Perfect
- Color: Blue, Violet, Light Blue, Dark Violet, Black.
- Density: 3.06 – 3.13, Average = 3.09
- Diaphaneity: Transparent to Translucent
- Habit: Prismatic – Crystals Shaped like Slender Prisms (e.g. tourmaline).
- Hardness: 5.5 – Knife Blade
- Luster: Vitreous (Glassy)
- Streak: bluish white
Occurrence: As metasomatic replacements near the outer margins of lithium-rich pegmatites.
It occurs as metasomatic replacements on the margins of lithium-rich pegmatites. Localities for Holmquistite are found in Sweden, Austria, the United States including here in the Black Hills of South Dakota in the Keystone area, Canada, Zimbabwe, South Africa, and Australia, among only a couple others.
Association: Quartz, clinoholmquistite, tourmaline, spodumene, plagioclase, biotite, clinozoisite, \hornblende.”