Holmquistite is a lithium magnesium aluminium inosilicate mineral with chemical formula: Li2(Mg,Fe2+)3Al2Si8O22(OH)2. It crystallizes in the orthorhombic crystal system as prismativ crystals up to 10 cm or as massive aggregates. It has a Mohs hardness of 5-6 and a specific gravity of 2.95 to 3.13.
Color could vary from black, dark violet to light sky blue.
Occurs as metasomatic replacements along the edges of lithium rich pegmatites.
It was first described from an occurrence in Utö, near Stockholm, Sweden. Named to honor the Swedish petrologist Per Johan Holmquist.