2012年（124）
分类： IT业界
2012-03-28 08:55:29
What is sandstone
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.
Sandstone is one of our most plentiful, widely distrubuted,
and useful building stones. Many fine public building are constructed with
various grades of construction quality sandstone. Some grades of sandstone are
also rather easy to carve into decorative forms. Depending upon the hardness and
texture, sandstone slabs can be carved into a variety of icons, decorations and
forms to enhance the walls, doorways and gateways of castles and other
buildings.
What is Slate?
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. At the same time the resulting intense
heat and pressure changed the orifional clay and silt particles into new
minerals such as mica, chlorite, and quartz. Slates vary in composition,
structure, color, and durability because of the degree to which their mineral
content has been altered and which is neither uniform nor consistant.
The
metamorphic process of geologic change necessary to produce slate are dependent
upon large scale movements in the earth's crest and the intense heat and extreme
pressure generated therein. For this reason, slate is found only in certain
mountainous regions of the earth. And only a few areas of these regions have
quarries that produce slate suitable for making slate stone for building
purposes.
There are three general classifications of slate: mica, clay and
igneous. For our discussion we will deal with the mice form. This is because
this slate is what slate roofs are made from. Mica is a generic term for any
group of minerals that crystallizes in thin easily separated layers. In slate,
the mineral is primarily silcon dioxide in the form of crystalline quartz.
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