Mylonite

Mylonite properties at a glance

Geology & background

Forms when rocks are intensely sheared and recrystallized in ductile fault zones, reducing grain size and producing a streaky or foliated fabric.

Mylonite is important for studying fault zones, mountain belts, and ductile deformation deep in the crust.

How to identify Mylonite

• Look for streaky, smeared, or strongly foliated fine-grained texture.
• Eye-shaped feldspar or quartz grains in a finer matrix can support mylonite.
• Mylonite is tied to fault-zone deformation rather than ordinary sedimentary bedding.
• Close-up photos of fabric are especially helpful for this name.

Where Mylonite is found

Reported from multiple metamorphic terrains worldwide; verify locality against specimen provenance when available.

How much is Mylonite worth?

Mylonite is usually valued for teaching, field context, locality, texture, mineral content, or unusually attractive specimens rather than high gem value.

Common uses

• Field identification
• Fault-zone study
• Structural geology
• Education

Interesting facts

• Mylonite records deep fault-zone deformation.
• Large original grains may survive as eye-shaped porphyroclasts.
• Its streaky fabric can reveal the direction of ancient shearing.

Care & safety

Mylonite can vary in toughness, cleavage, and weathering depending on mineral mix and fabric.

Avoid inhaling dust. Do not cut, grind, or polish unknown metamorphic rocks without eye protection and a properly rated respirator.

Related rocks & minerals

Quartz Quartz Family Feldspar Feldspar Group Chlorite Minerals Epidote Minerals Amphibolite Metamorphic Rocks Anthracite Metamorphic Rocks