Distinctive features:  
Colour, texture. Difficult to distinguish between the hornblende and pyroxenes because of their small grain size. The plagioclase occurs as thin laths. Pyrite, bronze biotite and iron oxide may be seen using a hand lens.

Colour: 
Medium grey to black.

Texture and granularity: 
Granular to fine grains. Occasionally porphyritic.

Composition: 
Pyroxene and plagioclase with larger amounts of pyroxene than plagioclase or equal amounts of both. Olivine is also often present, as well as grains of iron ore (magnetite and/or ilmenite) and bronze-coloured biolite.

Field associations: 
As dykes and sills, often of great thickness. It may pass into gabbro at depth (dolerite is the mdedium-grained equicalent of gabbro).

Varieties:
Olivine dolerite, which is dolerite, plus olivine pheonocrysts.

 

Worldwide, but particularly in Canada (Lake Superior), UK, USA (eastern states -- notably Pallisades Sill -- and western states as lava flows that merge into basalts).

 

Monumental, masonry, paving slabs, aggregate for roadstone.