Page 78 - Atlas of Sedimentary Rocks Under The Microscope

166, 167, 168 Carbonate rocks

D o l o m i t iza i o n
t
(continued)

166 shows a loosely-interlocking network of cuhcdral
dolomite crystals (unstained) with the intcrcrystal spaces
infillcd by a coarse sparry calcite cement (pink-stained).
Sometimes depositional textures arc preserved in a
rock despite complete replacement of the original sedi­
ment by dolomite. 167 shows a dolomite rock in which the
matrix has been replaced by more finely crystalline
dolomite than the allochems (perhaps originally ooids).
The result is a 'ghost' texture.
168 shows a highly porous dolomite rock, some of the
pores having been filled with a slightly fe rroan calcite
cement which is stained very pale mauve in thin section.
but is too f a int to reproduce well in the photograph. The
dolomite is very fine-grained and the outlines of original
allochems have been preserved as a ghost texture. Poros­
Ity in sediment replaced by dolomite is known as inter­
crptal porOSity (Fig. F. sec p. 65).

166: Stained thin section. Woo Dale Dolomite. Loll'er
Carlumi/eroll.\, C11nning Dale. Derbrshire. En�land: mag­
mfi<'lltton x 15. P PL.
167: Stained thin section. 011anamane F o rmation. M i d d l e
Jurassic. 011adim, Western High A tla� . Morocco: magn(( ­
ication x JJ. PPL.
168: Stained thin sec! ion. MuJ?nesian Limes/one, Permian.
Smllh )'orkshire, England: magnific(l/ioll x 38. PPL.

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