In geological terms more commonly used, rocks for surface plates are Granite, Diabase / Dolerite and Gabbro. Granite consists of a fairly coarse grained aggregate of quartz and feldspar with small quantity of black or white mica. More often granite is identified by shades like black, grey, pink, etc,. The other and rather more commonly used rock for surface plate is the Diabase or Dolerite.
The properties, which help in selecting a rock for manufacture of surface plates, are hardness, density and the grain size. Uniformity of grains and structure is also a good feature. In general fine-grained Dolerite has better scratch resisting property than harder grey granites,and this has been confirmed by scratch test using a sharp diamond.
Another important property of rocks is the density. The compressive strength of a rock increases with an increase in the density. This higher density rocks have generally smaller grains and lesser porosity. Dolerite stays ahead in this category with very fine and smaller grains when compared with other igneous rocks. Diabase / Dolerite is a variety of a stone type known as Gabbro.
While it is closely related to granite, it is not the same. Dolerite lacks several of the minerals (such as quartz and mica) which give granite its distinctive grain structure. The lack of quartz means that Dolerite is slightly less resistant to wear than the hardest granite. However, this is offset by the lack of mica, which is very soft, and tends to flake out of granite plates, leaving pits. Dolerite is denser than granite, weighing about 190 lbs. per cu.ft. While most granite weigh between 160-170 lbs. per cu.ft.
Dolerite is less porous and more stable, which means that a smoother and more uniform surface finish can be achieved. It can used for multi-dimensional, very high-accuracy applications that require a very smooth, stable surface like angle plates, parallels, master squares, straight edges and so on.
BEING LESS POROUS, IT ABSORBS LESS MOISTURE THAN GRANITE AND THEREFORE WARPS LESS.
A medium to coarse-grained intrusive igneous rock composed of potassium and sodium rich feldspar, quartz, minor plagioclase, and small amounts of ferromagnesian minerals such as biotite or hornblende. It is the intrusive equivalent of rhyolite.
When we inspect granite specimen it shows orange to pink feldspar, white plagioclase, grey quartz with minor dark mafic minerals. Another form of coarse-grained granite consisting of white feldspar, grey quartz and black biotite it also contains an inclusion of dark metamorphic rock.
The properties, which help in selecting a rock for manufacture of surface plates, are hardness, density and the grain size. Uniformity of grains and structure is also a good feature. In general fine-grained Dolerite has better scratch resisting property than harder grey granites,and this has been confirmed by scratch test using a sharp diamond.
Another important property of rocks is the density. The compressive strength of a rock increases with an increase in the density. This higher density rocks have generally smaller grains and lesser porosity. Dolerite stays ahead in this category with very fine and smaller grains when compared with other igneous rocks. Diabase / Dolerite is a variety of a stone type known as Gabbro.
While it is closely related to granite, it is not the same. Dolerite lacks several of the minerals (such as quartz and mica) which give granite its distinctive grain structure. The lack of quartz means that Dolerite is slightly less resistant to wear than the hardest granite. However, this is offset by the lack of mica, which is very soft, and tends to flake out of granite plates, leaving pits. Dolerite is denser than granite, weighing about 190 lbs. per cu.ft. While most granite weigh between 160-170 lbs. per cu.ft.
Dolerite is less porous and more stable, which means that a smoother and more uniform surface finish can be achieved. It can used for multi-dimensional, very high-accuracy applications that require a very smooth, stable surface like angle plates, parallels, master squares, straight edges and so on.
BEING LESS POROUS, IT ABSORBS LESS MOISTURE THAN GRANITE AND THEREFORE WARPS LESS.
A medium to coarse-grained intrusive igneous rock composed of potassium and sodium rich feldspar, quartz, minor plagioclase, and small amounts of ferromagnesian minerals such as biotite or hornblende. It is the intrusive equivalent of rhyolite.
When we inspect granite specimen it shows orange to pink feldspar, white plagioclase, grey quartz with minor dark mafic minerals. Another form of coarse-grained granite consisting of white feldspar, grey quartz and black biotite it also contains an inclusion of dark metamorphic rock.
AVERAGE CHEMICAL COMPOSITION OF GRANITE
| |
| Oxide |
Weight
|
| SiO2 | 70.18 |
| TiO2 | 0.39 |
| Al2O3 | 14.97 |
| Fe2O3 | 1.57 |
| FeO | 1.78 |
| MnO | 0.12 |
| MgO | 0.88 |
| CaO | 1.99 |
| Na2O | 3.48 |
| K2O | 4.11 |
| H2O+ | 0.84 |
| H2O- | 0.03 |
| P2O5 | 0.19 |
MAJOR INGREDIENTS OF GRANITE
|
|
| Quartz | 38.8% |
| Orthoclase | 16.7% |
| Albite | 28.3% |
| Anorthite | 9.2% |
| Corundum | 0.3% |
| Hyperthene | 4.3% |
| Ilmenite | 0.6% |
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