Lava is molten rock that flows from the bowels of the earth. Lava rock texture is divided into several forms that are influenced by the cooling rate and gas content in the magma.
Generally, lava can reach temperatures between 700°C and 1,300°C. The temperature difference in the lava depends on the mineral composition and viscosity.
Thin lava fluid will melt through the valley and solidify into rocks in the form of lava blocks. Meanwhile, if the liquid is slightly thick, it will form a dome with edges that resemble lava blocks.
Getting to Know the Characteristics of Lava Rock Texture
The shape of the lava flow from the volcano affects the physical characteristics of the lava. Thin basalt lava will spread widely to form flat land. Thicker rhyolite lava will form a collection of large boulders around the eruption area.
Physical Properties
Lava rock texture has the physical properties of volcanic rock with chemical composition, rock minerals, and petrogenesis. These properties are found in several types of volcanic rock, limestone, and quartz sandstone.
All three have chemical and mineral compositions with low levels of hydrous alumina silicate or clay. In addition, all three rocks also have high silica content.
Thus, rocks with these physical properties are difficult to change shape. Especially when reacting with fluids.
In terms of petrogenesis, volcanic rocks, limestone, and quartz sandstone come from the solidification of magma. In addition, these three rocks also come from sedimentation of hard grains with silica or mineral crystallization.
Texture
Lava rock texture is usually in the form of fine grains and consists of volcanic rocks that have glass. Usually, the texture of this rock is half glass or amorphous.
The weight of volcanic rocks with an amorphous texture is usually lighter. These rocks often contain clasts and phenocrysts of other rocks.
Phenocrysts are crystals that are larger than the matrix and can be seen with the naked eye. One example of phenocrysts is rhombic porphyry (rhombic porphyry).
For information, volcanic rocks often have a vesicle texture. This is because there are holes trapped in the molten lava.
One example of this rock is Pumice. The type of Pumice rock is the result of explosive volcanic eruptions.
Pumis or pumice is a textural term for volcanic rock which is solidified foamy lava. The lava is composed of glass pyroclastic with walls of extrusive volcanic igneous rock that bubbles.
Lava rock texture is divided into several types. One of them is the aphanitic texture and vesicular texture.
Aphanitic Texture
Aphanite is a fine-grained igneous rock, so that the constituent mineral crystals are invisible to the eye. This texture comes from rapid cooling in volcanic and hypabyssal environments.
Generally, the texture of Aphanite is not the same as volcanic glass such as obsidian. Volcanic glass is an amorphous product of magma that has undergone rapid cooling.
Usually, Aphanite is porphyry with large crystals embedded in a fine groundmass or matrix. For information, porphyry is a term in geology to describe igneous rocks with clear differences in the size of mineral crystals.
There are several types of rocks that have aphanitic properties. Among them are andesite, basalt, basanite, dacite, felsite, phonolite, rhyolite, and trachyte.
Vesicular Texture
Vesicular lava rock texture has the characteristics of rocks that are full of holes and cavities in their surfaces. This texture is often found in igneous rocks that appear on the earth’s surface after the extrusion process.
When magma rises to the surface, the pressure above it decreases. This condition causes the gas dissolved in the magma to come out, forming gas bubbles or cavities.
After the magma reaches the surface as lava and cools, the rock then freezes. This freezing process occurs around the gas bubbles that preserve them as holes called vesicles.
Vesicular textures are usually basalt or andesite, have cavities, and contain secondary minerals. Types of rocks with vesicular textures include pumice and scoria.
Lava rock textures have different forms depending on the cooling rate and gas content in the magma. Generally, thin or thick lava fluids will affect the type of rock characteristics that are formed.
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