Page 76 - Atlas of Sedimentary Rocks Under The Microscope

161, 162 Carbonate rocks
D o l o m i t i z a t i o n

{continued)

161 shows a dolomitic limestone containing 20 to 30%
dolomite. The dolomite is unstained and occurs as
cuhcdral rhomb-shapcd crystals which contain inclu­
sions. probably of calcite. and arc thus cloudy. The
unaltered limestone surrounding the dolomite is pink­
stained, non-ferroan calcite and shows a patchy texture of
micrite and spa rite with few recognizable grains. This is a
neomorphic fabric (p. 60).
162 shows a calcitic dolomite in which the original
calcite matrix has been wholly replaced by dolomite
(unstained) but the micritic allochems (peloids) have
resisted dolomitization and are only partly replaced
(dolomite unstained, calcite red). Where replacement is
incomplete, euhcdral rhomb-shaped crystals are visible.
Where replacement is complete, crystals have grown
together and the euhedral shape is lost.

161: Stained thin section, Woo Dale Limesrone, Lower
Carboniferous. Derbyshire, England; magnification x 20.
PPL.
162: Stained thin section. Middle Jurassic. Jebel Amsiuen.
Morocco; magnification x 14. PPL.

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