What is Kaersutite?
Kaersutite is a titanium-rich amphibole found in alkaline volcanic rocks, recognised by dark prismatic crystals and its value in reading magma evolution.
Mineralogy and crystal structure
Reference formula: NaCa2(Mg4Ti)(Si6Al2)O22O2. Kaersutite has a monoclinic double-chain amphibole structure and substantial Ti substitution. Natural compositions vary in alkali, iron, titanium and halogen content, so the COD model is a representative natural kaersutite analysis. Kaersutite is classified with silicates and has a monoclinic crystal system. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 3.3–3.5.
Colour, lustre and habit
Typical colours include black, brown-black, dark green. The usual prismatic, granular, massive habit and vitreous, sub-metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Kaersutite forms in or is associated with alkaline basalts, volcanic xenoliths and metasomatised mantle-derived rocks. Important documented localities include Iceland, the Czech Republic, Italy, Japan, Canada and the United States.
A dark amphibole with a volcanic fingerprint
Kaersutite is a powerful cabinet mineral for anyone interested in volcanic rocks. Its dark crystals are visually strong, while the titanium-rich chemistry gives the specimen a more specialised story than colour alone can provide.
Collecting and care
Protect amphibole cleavage and keep the volcanic host with the specimen; avoid disturbing fibrous fragments.
