Migmatite
Image: No machine-readable author provided. <a href="//commons.wikimedia.org/wiki/User:Siim" title="User:Siim">Siim</a> assumed (based on copyright claims). (CC BY-SA 3.0)
Mineral NameMigmatite
Chemical FormulaVariable (composed of multiple minerals)
Mohs HardnessVariable (typically 6-7 for felsic minerals, 2.5-3 for micas)
Streak ColorVariable (not typically used for rocks)
CleavageVariable (depends on constituent minerals, e.g., perfect in micas, good in feldspars)
FractureUneven to conchoidal (depends on constituent minerals)
Specific GravityVariable (typically 2.6-3.0)
Colorswhite, light grey, dark grey, black, pink
TransparencyOpaque to translucent (depending on constituent minerals)
Type LocalityGeirangerfjord, Norway
Mineral GroupMetamorphic rock
Usesbuilding material, decorative stone, geological study
Associated Mineralsquartz, feldspar, biotite, muscovite, garnet, sillimanite
Raritycommon
Description
A banded rock characterized by alternating light-colored (felsic) igneous-looking layers and dark-colored (mafic) metamorphic layers, often displaying complex, wavy, or ptygmatic folds.
Geological Context
Migmatites form under extreme high-grade metamorphic conditions where partial melting of the protolith occurs, creating a rock that is a mixture of metamorphic rock and newly crystallized igneous material. They represent the transition zone between metamorphic and igneous rocks.
