# Cleavage versus fracture

Canonical page: https://lithomap.app/resources/field-tests/cleavage-vs-fracture
Last reviewed: September 18, 2026
Page purpose: Original LithoMap field-method reference for human readers, search systems, and language models.

## Direct answer

Look for repeated, parallel break surfaces that recur in one or more directions. Cleavage follows structural weakness in a mineral; fracture is irregular breakage where no cleavage plane controls the surface. Crystal faces and cleavage surfaces are not the same thing.

## Why the test works

A crystal lattice may contain directions where atomic bonds are weaker. Breakage along those directions produces cleavage planes with repeatable geometry.

Minerals without useful cleavage may break by conchoidal, uneven, splintery, or earthy fracture. A sample can display both cleavage and fracture on different surfaces.

## Field kit

- Bright directional light
- 10× hand lens
- Existing broken specimen
- Angle card or simple protractor for approximate geometry
- Eye protection if an authorized fresh break is necessary

## Procedure

1. Observe before breaking: Rotate the specimen under a single light. Search existing chips for flat reflections that flash together.
2. Find repetition: A single plane may be a crystal face or accidental break. Cleavage is supported when several parallel surfaces recur through the same mineral.
3. Count directions: Group parallel planes as one direction. Then look for a second or third nonparallel set.
4. Estimate angles: Note whether directions meet near 90 degrees or at distinctly oblique angles. Do not demand perfect geometry from a rough hand sample.
5. Record fracture too: Describe curved shell-like, uneven, splintery, or earthy surfaces where cleavage is absent or interrupted.

## Interpreting results

- One excellent direction; thin elastic or flexible sheets: Characteristic of mica-group minerals, though sheet behavior and color still matter.
- Two directions near 90 degrees: Common in feldspars and pyroxenes. Striations, angle precision, color, and hardness help separate them.
- Two directions near 60 and 120 degrees: Supports amphibole-group minerals such as hornblende.
- Three directions at 90 degrees: Cubic cleavage, seen in minerals such as halite and galena.
- Three directions not at 90 degrees: Rhombohedral cleavage, typical of calcite and dolomite.
- Smooth curved, shell-like surfaces: Conchoidal fracture supports quartz or glass, but does not distinguish natural material from manufactured glass by itself.

## Examples and related guides

- Muscovite: One perfect basal cleavage that produces thin sheets. — https://lithomap.app/resources/mineral-identification/muscovite
- Galena: Three excellent cleavage directions near 90 degrees. — https://lithomap.app/resources/mineral-identification/galena
- Calcite: Three cleavage directions that form rhombohedra rather than cubes. — https://lithomap.app/resources/mineral-identification/calcite
- Quartz: No cleavage; commonly breaks with conchoidal fracture. — https://lithomap.app/resources/mineral-identification/quartz

## Common mistakes

- Calling a crystal growth face cleavage
- Counting each parallel surface as a separate direction
- Judging the angle from one distorted chip
- Assuming every shiny plane is cleavage
- Breaking a specimen before inspecting surfaces that already exist

## Safety and limitations

- Prefer existing broken surfaces. Do not strike a specimen unless you own it, have permission, and can control flying chips.
- Wear eye protection and keep other people clear of the work area.
- Do not break fibrous, dusty, sulfide-rich, lead-bearing, radioactive, or culturally significant material.
- Breakage is destructive and cannot prove a mineral identity on its own.

## Frequently asked questions

### Is a flat crystal face the same as cleavage?

No. A crystal face formed during growth; cleavage formed during breakage. Cleavage is identified by repeated parallel surfaces within broken material, not by flatness alone.

### Can a mineral have both cleavage and fracture?

Yes. A break may follow cleavage in one area and cross the structure irregularly elsewhere, especially in small, intergrown, or weathered grains.

### Why are cleavage angles approximate in hand samples?

Surfaces may be incomplete, stepped, altered, or partly hidden by other minerals. Use angle categories together with hardness, habit, and other properties.

## Authoritative sources

- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Geology Lesson 2: Global Building Blocks — U.S. National Park Service: https://www.nps.gov/teachers/classrooms/geology-lesson-2-global-building-blocks.htm
- Kansas Rocks and Minerals: Mineral Identification — Kansas Geological Survey: https://www.kgs.ku.edu/Publications/Bulletins/ED2/07_ident.html

This method supports preliminary field identification. It is not laboratory confirmation, appraisal, hazard clearance, proof of origin, or permission to collect or alter a specimen.