Contact hornfeld is a metamorphic rock formed during heating ( contact metamorphism ) of rocks by intrusion .
The hornfelses usually have a fine-grained, full-crystalline granoblast or porphyroblastic structure. The texture is massive or banded (inheriting protolith stratification), sometimes spotty. The main tissue of the breed is an aggregate of quartz , calcite , biotite , muscovite , epidote , albite , hornblende, sillimanite , carbonaceous matter and sulfides indistinguishable to the eye.
Porphyroblasts are usually represented by andalusite , cordierite , garnet of almandine-spessartine composition, sometimes biotite, staurolite , feldspars, hornblende, etc.
The color of the hornfelses is diverse. Gray, white, yellowish (quartz, andalusite, muscovite, etc.), green ( chlorite , epidote ), black (carbonaceous) colors predominate. The distribution of color is uniform or spotty and banded. The breed is strong. The fracture is uneven, conchoid (horny). Keratinization is a sign of hot intrusive contact and evidence of an older age of keratinized rocks in relation to intrusion.
Where meets
Due to attachment to plutonic intrusions, the hornfelses lie near plutonic rocks. Significant deposits of hornfelses are in Canada, the USA, Russia, South Africa, Norway and Sweden. [one]
Notes
- ↑ Contact metamorphism. Rogoviks Archived February 21, 2014 on Wayback Machine All Minerals.