2012年(124)
分类: IT业界
2012-03-27 13:58:04
Sedimentary Rocks: Limestone and Sandstone
Metamorphic Rocks: Slate and
Marble
Igneous Rock: Granite
Miscellanous: Field and river
rock
Limestone is a sedimentary rock consisting primarily of lime which was
formed by a variety of biological, chemical and physical processes that took
place over millions of years. Generally most limestone is chiefly composed of
calcium carbonate, the organic remains of shells and coral.
Dolomitic
limestones are chemically magnesium carbonate. The fossils and other sedimentary
structures which limestone contains provides a key as to the environment in
which limestones where formed.
Limestone used outside must be protected from
water and frost damage. If the porosity of the stone is to high, water may
collect in the stone, freeze, and then swell. This may cause the stone to flake,
crack or to split.
Limestone is also used to make lime cement. This process
involves burning the limestone in kilms to produce the lime cement. And this
lime cement when mixed with sand and water would be used to cement the building
stones or fired clay bricks together to form walls and other parts of the
castle. This process of making and using lime cement will be discused in detail
later.
Sandstone is a sedimentary rock consisting primarily of quartz,
occasionally felspar and other sand particles, and small rock particles all
cemented together into a firm stone. These materials eroded from older rocks
were sorted and deposited by rain and wind to form beds of layered materials.
The sandstone was then formed by a chemical and physical process similar to the
formation of limestone. The various minerals, such as iron oxides and
carbonates, that leached into the layered sand beds gives sandstone its rich and
varied colors.
Slate is a metamorphic rock. This means that this fine grained
rock is the result of the actions of pressure, heat and water upon clay and silt
sediments deposited on ancient sea beds over millions of years ago. Mountain
building forces subsequently gradually folded, crumpled and compressed these
deposits into the shale. This has resulted in a very compact and highly
crystalline rock structure.
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