Granofels

Granofels

Metamorphic rock
Granofels sample showing granoblastic texture
Composition
Variable
Texture	Granoblastic

Granofels is a term referring to medium- to coarse-grained metamorphic rocks which have a granoblastic texture (having poorly formed, equi-granular crystal grains visible to the naked eye) and lack distinct foliation or lineation. ^[1] The granofels term encompasses rocks which are known under more specific names, such as marble or hornfels. ^[2]

Formation

Granofels forms under medium- to high-grade metamorphic conditions, typically involving elevated temperatures and pressures that promote recrystallization of minerals without inducing directional stress. This process results in a granoblastic texture, characterized by equigranular, interlocking mineral grains lacking foliation. ^[2]

Examples

Granofels is a general term that includes several more specific rock types:

• Marble – formed from the metamorphism of limestone, composed primarily of recrystallized calcite or dolomite
• Hornfels – produced by contact metamorphism of shale or other fine-grained sedimentary rocks, often containing quartz, feldspar, and mica
• Quartzite – derived from sandstone, sometimes classified as granofels when texture is granoblastic and non-directional

These examples illustrate the diversity of protoliths and mineral compositions that can result in granofelsic textures.

References

1. Goldsmith, Richard (1959). "Granofels, a New Metamorphic Rock Name". The Journal of Geology. 67 (1): 109–110. Bibcode:1959JG.....67..109G. doi:10.1086/626561.
2. Schmi, Rolf; Fettes, Douglas; Harte, Ben; Davis, Eleutheria; Desmons, Jacqueline (2007). "How to name a metamorphic rock". British Geological Survey.