Jun 6 2014
Hornfels are a type of metamorphic rock, having a dense, compact, and fine grained structure. The formation of these rocks is the result of contact metamorphism of shales and basalts. In some type of hornfels, distinctive rounded patches, composed of coarse-crystalline material, are seen; these are called spotted hornfels. Hornfels exhibit a non-directional structure.
The name of this rock is derived from the German, meaning hornstone.
Appearance and Physical Characteristics
The physical characteristics of hornfels are provided below:
- Structure – non-foliated, very fine grained, and non-crystalline
- Color – mottled brownish-green, dark brown to black
- Composition – variable
- Toughness – very hard
- Parent rocks – shale or mudstone
- Occurrence – adjacent to igneous rock intrusion at shallow depths
- Special features – acoustic in nature, produce resonance when struck
Types of Hornfels
There are many types of hornfels, which are named based on their composition. Some of the common types of hornfels are tremolite, wollastonite, calc-silicate, adalusite, kyanite, garnet and skarn, epidote, pyroxene, and cordierite.
References