Mineral Guide · Mineral

Grunerite

Grunerite is an iron-rich amphibole found in metamorphosed iron formations and other iron-rich metamorphic rocks.

Interactive 3D structure

Crystal structure

Open COD source

Loading interactive structure...

Rotate with the mouse or touch. The cell frame and a, b, c labels show the repeating unit used by the structure model.

Mineral properties

Formula: Fe₇Si₈O₂₂(OH)₂
Class: Silicates
Crystal system: Monoclinic
Typical colours: black, brown, green-brown, grey-green
Lustre: Pearly, Vitreous
Hardness: 5.00-6.00
Specific gravity: 3.40-3.60
Crystal habit: Fibrous, Granular, Prismatic
Origin: banded iron formations, iron-rich schists, gneisses and metamorphic iron deposits

What is Grunerite?

Grunerite is an iron-rich amphibole found in metamorphosed iron formations and other iron-rich metamorphic rocks.

Mineralogy and structure

Reference formula: Fe₇Si₈O₂₂(OH)₂. Grunerite has the monoclinic amphibole structure and forms a compositional series with cummingtonite. Fibrous material should be handled as a mineralogical specimen, not disturbed. Grunerite belongs to the silicates and has a monoclinic crystal system. Typical hardness is 5–6 on the Mohs scale and specific gravity is approximately 3.4–3.6.

Colour and appearance

Typical colours include brown, grey-green, black, green-brown. The usual fibrous, prismatic, granular habit and vitreous, pearly lustre are useful descriptive features, but colour alone is not diagnostic.

Formation and localities

Grunerite forms in or is associated with banded iron formations, iron-rich schists, gneisses and metamorphic iron deposits. Important documented localities include the United States, Canada, Sweden, South Africa, Brazil and Australia.

Collecting and care

Keep fibrous aggregates intact and avoid cutting, grinding or creating airborne dust.

Sources and editorial review

Reviewed by NotOnlyRocks Editorial Team

Last reviewed: 31 August 2026

All mineral guides

Looking for Grunerite?

We don't currently have Grunerite specimens available.

Send us a request and we will try to find a suitable specimen for you.

Request Grunerite