# How to identify staurolite

Canonical page: https://lithomap.app/resources/mineral-identification/staurolite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap mineral identification reference for field observations, search systems, and language models.
Classification: Iron magnesium aluminum silicate hydroxide

## Summary

Staurolite is a brown to reddish-brown metamorphic mineral known for prismatic crystals and distinctive cross-shaped twins, with hardness near 7 to 7.5 and a pale streak.

## Quick identification clues

- Brown, reddish-brown, or nearly black
- Prismatic crystals with common cross-shaped twins
- Mohs hardness about 7 to 7.5
- Occurs chiefly in mica schist and gneiss

## Composition and classification

Staurolite is a complex iron-, magnesium-, and aluminum-bearing silicate hydroxide with variable substitutions. Its exact formula and composition can vary among specimens.

## Appearance

Crystals are commonly stout prisms with rough surfaces and resinous to subvitreous luster. Penetration twins may form crosses intersecting near 60 or 90 degrees.

Untwinned crystals, broken grains, and matrix-bound porphyroblasts may lack the famous cross and resemble garnet, tourmaline, or dark metamorphic minerals.

## Identification tests

- Hardness: About 7 to 7.5. Scratches glass and is not readily scratched by steel.
- Habit: Stout prismatic crystals, commonly twinned. Cross twins are highly characteristic but not universal.
- Cleavage: Poor. Broken surfaces are uneven rather than dominated by repeated cleavage.
- Streak: White to grayish. Separates it from dark-streaking metallic minerals.

## Common lookalikes

- Garnet: Usually equant with dodecahedral or rounded forms rather than prismatic cross twins.
- Tourmaline: Commonly longer, strongly striated, and triangular in cross section.
- Manufactured or carved cross: May show tool marks, unnatural symmetry, or lack a metamorphic matrix and crystal surfaces.

## Direct side-by-side comparisons

- Staurolite vs. garnet — https://lithomap.app/resources/mineral-identification/compare/staurolite-vs-garnet

## Most relevant related guides

- Garnet — https://lithomap.app/resources/mineral-identification/garnet
- Tourmaline — https://lithomap.app/resources/mineral-identification/tourmaline
- Apatite — https://lithomap.app/resources/mineral-identification/apatite
- Augite — https://lithomap.app/resources/mineral-identification/augite

## Formation

Staurolite forms during medium-grade regional metamorphism of aluminum-rich sedimentary rocks.

It commonly occurs with mica, garnet, kyanite, quartz, and other index minerals used to interpret metamorphic conditions.

## Occurrence and geologic setting

Staurolite is characteristic of selected metamorphic belts and occurs in schist and gneiss across parts of the Appalachians, New England, the southern Rocky Mountains, and other regions.

A cross-shaped object should be evaluated for natural crystal faces and lawful provenance rather than assumed to be a natural twin.

## Uses and significance

Staurolite is chiefly a collector mineral and metamorphic indicator. Cross twins are sold as “fairy stones,” but commercial pieces may be altered, mounted, or manufactured.

## Field safety and limitations

- Do not pry crystals from outcrops or damage protected sites.
- Cross shape is strong evidence only when natural crystal texture is present.
- Avoid destructive testing of complete twins.

## Authoritative sources

- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Mohs Hardness Scale — U.S. National Park Service: https://www.nps.gov/articles/mohs-hardness-scale.htm
- Natural Gemstones: Mineral Gemstones — U.S. Geological Survey: https://pubs.usgs.gov/gip/gemstones/mineral.html

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/minerals/staurolite.webp
- Description: Reddish-brown cross-shaped twinned staurolite specimen displayed on a pale base
- Creator: 384
- License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/
- Source record: https://commons.wikimedia.org/wiki/File:Staurolite_specimen.jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.