mylonite
Very LowTechnical / Academic (Geology)
Definition
Meaning
A fine-grained, foliated metamorphic rock formed by ductile deformation and dynamic recrystallization, often associated with fault zones.
In geology, it refers specifically to a tectonite formed by extreme shearing in fault zones, characterized by a flinty texture and millimetre-scale layering.
Linguistics
Semantic Notes
This is a technical term in structural geology and petrology. It denotes not just any crushed rock, but one with a characteristic microscopic fabric resulting from plastic flow and recrystallization under stress.
Dialectal Variation
British vs American Usage
Differences
No significant difference in meaning. Spelling and pronunciation are identical.
Connotations
None beyond its strict geological definition.
Frequency
Equally rare and specialized in both UK and US contexts, used exclusively within geology.
Vocabulary
Collocations
Grammar
Valency Patterns
[Noun] is a mylonite.The [feature] consists of mylonite.Mylonite [verb] in the shear zone.Mylonite formed from [protolith].Vocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Usage
Context Usage
Business
Never used.
Academic
Exclusive to geological research papers, textbooks, and field studies describing rock deformation.
Everyday
Virtually never used.
Technical
Core term in structural geology, petrology, and tectonic studies for describing deformed rocks in fault zones.
Examples
By Part of Speech
adjective
British English
- The mylonitic fabric was clearly visible under the microscope.
- They mapped the mylonitic shear zone.
American English
- The mylonitic texture indicated high strain.
- The unit contains mylonitic gneiss.
Examples
By CEFR Level
- Geologists sometimes find very hard, striped rocks called mylonite.
- The fault core is composed of a dark, fine-grained mylonite formed from the original granite.
- Microstructural analysis of the ultramylonite reveals evidence of dominant grain boundary sliding and dynamic recrystallization.
Learning
Memory Aids
Mnemonic
Think: 'MY rock is ground to a fine LONgITE' – mylonite is rock ground fine by long-term shearing.
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Do not confuse with 'melanite' (a type of garnet). The Russian equivalent is 'милонит' (milonit).
Common Mistakes
- Confusing it with 'melanite' (a mineral).
- Using it to refer to any crushed or brecciated rock without the characteristic recrystallized fabric.
- Misspelling as 'mylonight' or 'myloanite'.
Practice
Quiz
Mylonite is primarily associated with which geological feature?
FAQ
Frequently Asked Questions
Mylonite is a metamorphic rock. It forms when existing rocks are deformed by intense shearing, a process called dynamic metamorphism.
Both are fault rocks, but mylonite forms by ductile deformation involving plastic flow and recrystallization, giving it a foliated texture. Cataclasite forms by brittle fracturing and crushing (cataclasis) with little to no recrystallization.
Yes, hand specimens of mylonite are common. They are typically hard, dense, and have a distinctive streaky or banded appearance (foliation) on a millimetre scale.
It comes from the Greek 'mylōn', meaning 'mill' (as in a grinding mill), referring to the finely ground, milled texture of the rock.