Geoscience Reference
In-Depth Information
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'Huddleston' dolomitic limestone (Yorkshire,
England) consisting mainly of dolomite crystals (pink).
Macropores are shown black; XPT, ×35.
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'Highmoor' dolomitic limestone (Yorkshire,
England) consisting of dolomite crystals (grey) with a
cellular structure. Macropores are shown yellow; PPT,
×150.
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Travertine (Turkey) consisting a calcite crystals
(light brown) and including small irregular cavities
(yellow); PPT, ×35.
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Travertine consisting of calcite (pink) with distinct
banding; XPT, ×35.
Figure
71
shows 'Huddleston', which is a dolomitic
limestone with a coarsely crystalline, porous texture.
Figure
72
shows 'Highmoor', which has a highly porous,
cellular texture that represents an original ooidal/peloidal
fabric in which the cores of the spheroidal framework
grains have been leached out.
Travertine is a porous but overall well consolidated
calcitic limestone, which forms around springs. It is used
for masonry locally, and exported for flooring and lining.
It is typically whitish, yellow to brown, banded, and
compact, with some characteristic irregular cavities.
Figure
73
shows a sample of travertine that has been cut
parallel to the banding, while Figure
74
shows a different
travertine sample that has been cut across the banding.
Onyx-marble is an exceptionally fine-grained,
generally translucent and banded variety of calcite that
forms at warm springs. It is used for decorative purposes.
Figure
75
shows an onyx-marble that is translucent
green with brown banding in hand specimen.
O
THER SEDIMENTARY ROCKS
An ironstone (
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) is a sedimentary rock that contains
more than 15% iron, which may be present as variable
proportions of iron-bearing minerals such as goethite,
