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Definition: diabase from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

Alternative name for dolerite (a form of basalt that contains very little silica), especially dolerite that has metamorphosed.


Summary Article: Dolerite
from Rock and Gem

DOLERITE IS EQUIVALENT to basalt and gabbro in composition, although it is intermediate between them in grain size. A fine- to medium-grained rock, dolerite is from one-third to two-thirds calcium-rich plagioclase feldspar, the remainder being principally pyroxene. It has a silica content of less than 55 per cent, and its quartz content is usually less than 10 per cent. Magnetite and olivine may be present: if olivine is present, the rock is called olivine-dolerite. Extremely hard and tough, it occurs in dikes and sills intruded into fissures in other rocks.

  • Properties
  • Rock type Mafic, plutonic, igneous
  • Major minerals Calcium plagioclase, pyroxene
  • Minor minerals Quartz, magnetite, olivine
  • Color Dark gray to black, often mottled white
  • Texture Fine to medium
Ancient building stone

The dolerite “bluestones” of the inner circle of Stonehenge were transported 240 miles (385km) from Wales to Wiltshire in England. They were brought by sea, river, and over land. Exactly what significance was attached by the builders to this particular stone is unknown, but it must have been considerable to justify the enormous effort required to get the bluestones to the site. Stonehenge was constructed in 3000–2000BC.

Stonehenge

The bluestone used for making the stone circle of Stonehenge originated at Carn Meini Quarry in Wales.

© 2008 Dorling Kindersley Limited

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