Dolerite
Dolerite is a medium grained mafic intrusive rock and it is sometimes called diabase. It has some similarity with basalt, but on this type of rock the crystals can be spotted with a hand lens. Dolerite has also a similar composition to gabbro, but gabbro has larger crystals. Dolerites can be found in sills, dikes, lopoliths or laccoliths which cooled slowly.
Characteristics
Dolerite is made up from feldspar and pyroxene minerals. The feldspar can be present in a fraction varying from 40 to 70 percent of the rock. Moreover some olivine can be present giving this grey to black rock a greenish glow. Dolerite is an intrusive rock which means phenocrysts can be present. This are large crystals suspended in a matrix of fine crystals. These are present due to mixing of other rocks into the cooling parent magma. The formation of dolerite has two requirements, namely:
- A basaltic magma source
- Shallow emplacement and cooling in a relatively small subsurface structure such as a sill, dike, lopolith or laccolith.
References
Dolerite
| Type | Extrusive igneous rock |
|---|---|
| Clasts | Medium grained |
| Hardness | Very hard |
| Color | grey to black with greenish luster |
| Minerals | Feldspar and pyroxene minerals |
| Touch | Rough |
| Image | Dolerite |