The disadvantage of limestone is that it is soft and not wear-resistant. If limestone is made into a stone mill, the ground grain will contain a lot of limestone powder, and such grain is inedible.
granite
Granite is a kind of tectonic rock formed by volcanic lava rising to the surface of the earth's crust in a molten state under considerable pressure. Magma does not gush out from underground, but slowly cools and solidifies underground. It is a kind of deep acid igneous rock, belonging to igneous rock. Granite is mainly composed of quartz, feldspar and mica. Among them, the content of feldspar is 40%-60%, and the timely content is 20%-40%, and its color depends on the type and quantity of components. This rock is hard and dense.
I. Composition
Granite is a hard crystalline stone formed by igneous rocks. It was originally composed of feldspar and quartz, mixed with one or more black minerals, and arranged evenly in structure.
Granite is mainly composed of quartz, feldspar and mica. Among them, the content of feldspar is 40%-60%, and the timely content is 20%-40%, and its color depends on the type and quantity of components. Granite is a completely crystalline rock. High-quality granite has fine and uniform particles, compact structure, high timely content and bright feldspar luster.
Granite has a high content of silica and belongs to acidic rocks. Some granites contain trace radioactive elements, so indoor use should be avoided. Granite has compact structure, hard texture, good acid and alkali resistance and weather resistance, and can be used outdoors for a long time.
Second, classification
Granite has many kinds and classification methods because of its complex composition and diverse formation conditions.
1, depending on the kind of minerals contained.
Divided into black granite, muscovite granite, amphibole granite, mica granite, etc.
2. According to the structure.
It can be divided into fine-grained granite, medium-grained granite, coarse-grained granite, porphyritic granite, porphyritic granite, geode granite and gneiss granite.
3, according to the mineral content
It can be divided into cassiterite granite, niobite granite, beryllium granite, lepidolite granite and tourmaline granite. Ordinary petrochemical, Yunyinghua, electro-petrochemical and other automatic deformation.
Third, characteristics
Granite has compact structure, high compressive strength, low water absorption, high surface hardness, good chemical stability and durability, but poor fire resistance.
Granite has a fine, medium and coarse grain structure, or a mottled structure, with uniform and fine grains, small voids (porosity is generally 0.3% ~ 0.7%), low water absorption (water absorption is generally 0. 15% ~ 0.46%) and good frost resistance.
Granite has high hardness, Mohs hardness is about 6, density is between 2.63g/cm3 and 2.75g/cm3, and compressive strength is 100-300MPa, in which fine-grained granite can reach 300MPa, and bending strength is generally 10-30mpa. Granite often occurs in the form of bedrock, rock plant and rock block. , and controlled by regional tectonics. Generally, it is relatively large in scale and widely distributed, so it is convenient to mine and easy to produce large materials. Its regular joint development is conducive to mining stones with regular shapes.
Granite has high yield, can be processed in many ways, and has good splicing. There is also granite, which is not easy to weather and can be used as outdoor decorative stone.
Granite has a uniform texture. Although its color is mainly light, it is also rich in red, white, yellow, green, black, purple, brown, beige, blue, etc., and its color changes little, so it is suitable for large-scale use.