Dorrite

Dorrite is a porphyritic igneous rock characterized by the presence of plagioclase phenocrysts (large, visible crystals) set in a finer-grained groundmass, also primarily composed of plagioclase and often containing other minerals such as pyroxene and olivine. It is a relatively rare rock type and is typically associated with alkaline magmatism.

The term "dorrite" was originally used to describe rocks from the D'orr region of France. Its classification can be somewhat ambiguous as it lies along a continuum with other similar rock types like anorthosite and gabbro. The relative abundance and type of the constituent minerals help to differentiate dorrite from these other rocks. Specifically, dorrite is characterized by its significant plagioclase content and porphyritic texture.

Dorrites are often dark in color, reflecting the presence of ferromagnesian minerals. Geologically, they can provide insights into the cooling and crystallization history of the magma from which they formed. The presence of phenocrysts suggests a two-stage cooling process, where initial crystallization occurred at depth, followed by more rapid cooling closer to the surface.

Due to its relative rarity, dorrite does not have widespread economic uses. However, like other igneous rocks, it can be used as a source of building materials or aggregate. The presence of specific minerals within dorrite might also be of interest for research purposes.

The classification of dorrite can be further refined by specifying the type of plagioclase (e.g., labradorite dorrite, andesine dorrite) or by identifying any significant accessory minerals present. Microscopic analysis is often required for accurate identification and classification.