Types of the volcanic rocks

Micropore rocks

The pores of the volcanic rocks are very small. The pores of the rocks are as big as the tips, well distributed and gray, and the rocks are called the “Micropore rock”.

Small-hole rocks

The kind of volcanic rocks are sponge like, and the holes are as big as sesame to rice and well distributed. This type of the rocks is good looking, so they are the most popular rocks in the Yunnan Tengchong volcanic rocks in the market, and the production of the rocks is greatest. They are distinguished by color, such as “Black small-hole” and “Gray small-hole” rocks. The “Black small-hole” rocks are blacker than the kinds of rocks from Heilongjiang and Yunnan province, which is why they are so popular in the market these years, especially in Chengdu, Chongqing, Jiangsu, Shanghai, Zhejiang and Tianjin, etc. Here is a photo of the “Black small-hole” rocks from Yunnan.

Mid-hole rocks

The holes of this kind of rocks are middle size and honeycomb like. The rocks have special artistic effects, especially in some artworks.

Big-hole rocks

The holes of this kind of the rocks are big and not well distributed. The kinds of rocks are used in some artworks.

Red volcanic rocks

Red volcanic rocks are formed by the coagulation of the residual magma after the volcanic eruption, dark red, and light even floating on the water, called “pumices”. As a short development period, the proved reserves of the red volcanic rocks from Yunnan Tengchong are huge, and there is enormous room for the development of the red volcanic rocks.

These kinds of rocks are used in industry and agriculture, and the rocks from Yunnan Tengchong are mainly used in some artworks. As the crust can keep warm, so the temperature is higher when it is closer to the earth core. The earth core is solid under the high pressure. The high temperature fluid substances under the crust are the magma. According to the magma from the volcanic eruption, the silicates are the main part of the magma, in which the content of SiO2 is 30%~80%, the content of the metal oxides such as Ai2O3, Fe2O3, FeO, MgO, CaO and Na2O, etc is 20%~60%, and the content of other substances such as heavy metal, nonferrous metals, rare metals and radioactive elements, etc is less than 5%. There are some other volatile substances such as H2O, CO2, H2S, F and Cl etc in the magma.

Formation of the magmatic rocks

The formation of the magmatic rock has two ways: invasion and ejection. The magma under the crust cooling down slowly is called “Invasion magmatic rock”. The formation of this kind of rocks takes a long time. The formation of 2,000 meters thick granite mass maybe takes 64,000 years. The magma ejects out of the crust and cools down to form the “Ejection magmatic rock”. The period to form an “Ejection magmatic rock” is not too long as the temperature cooled down rapidly. One meter thick basalt needs 12 days, ten meters thick basalt needs three years and seven hundred meters thick basalt needs 9,000 years, which shows that the formation time of the “Invasion magmatic rock” is much longer than that of the “Ejection magmatic rock”.

Viscosity is another important property of the magma, and it represents the status and degree of the flow of the magma. The content of the SiO2 in the magma is an important factor to the viscosity, and also the Al2O3 and Cr2O3, that higher the content is, higher the viscosity of the magma is. The volatile components in the magma can decrease the viscosity and the melting point of the magma, and make the magma flow easily and a longer crystallization period. The higher the temperature of the magma is, the lower the viscosity of the magma is; the higher the pressure of the magma is, the higher viscosity of the magma is.

Magmatic rocks have their own structures, for example, the “Ejection magmatic rock” will be porous when the temperature and the pressure decrease rapidly to make the quick air evolution. If they have rich porous structures, the rocks will be so light that they can float on the water, called “pumices”. If these pores are filled with some other substances, they may form the amygdaloidal structures. If the magma ejects out of the crust, there will be some traces when the magma flows, like ropes screwing together, called fluidal structures or ropy structures. If the magma ejects out under the water, there will be some ellipsoid rocks, called pillow structures. It is clear that all of these structures just exist in the magmatic rocks.

Either the “Invasion magmatic rock” or the “Ejection magmatic rock” is very clear from the rocks around them. If the magma injects along the gap of the bedding, it will form an intrusion such as rock basin, rock sill or rock loccolith, and the textures of the magmatic rocks are parallel with their neighbors, called “concordant intrusion”; the magma doesn’t inject along the gap of the bedding, and it go through the texture of the surrounding rocks, that is called “Nonconformity intrusion”. The rock walls are the plate intrusions through the rock stratums straightly, with the thickness of tens of centimeters, tens of meters, tens of kilometers or hundreds of kilometers.