Actually, obsidian doesn't have grains at all. Technically obsidian is a glass, which means it has no internal structure. When geologists refer the the grain size of a rock, they mean how big the crystals that make it up are. Since obsidian has no crystals, it therefore has no grain size.
Obsidian has a small grain size due to its volcanic origin, which means that it cools quickly and does not have time to form large crystals. It is typically fine-grained and exhibits a glassy appearance.
Obsidian is an extrusive igneous rock that forms when lava cools quickly and solidifies into a glass-like material without crystal formation. It is typically black in color and has a smooth, glassy texture due to its rapid cooling process.
Obsidian cooled very quickly. It's a vulcanic glass, meaning that the crystals are so small, they had virtually no time to form an orderly crystalline texture, and are basically placed randomly. Smaller grain size is associated with faster cooling.
The black volcanic rock with small crystals is most likely basalt. Basalt is fine-grained and is commonly found in volcanic regions as a result of solidified lava flows. The small crystals are often composed of minerals such as plagioclase and pyroxene.
Obsidian cools rapidly, preventing large crystals from forming. As a result, the mineral crystals are too small to be seen with the naked eye. The rapid cooling process hinders the growth of crystals, resulting in a smooth and glassy texture.
Obsidian has a small grain size due to its volcanic origin, which means that it cools quickly and does not have time to form large crystals. It is typically fine-grained and exhibits a glassy appearance.
Obsidian is an extrusive igneous rock that forms when lava cools quickly and solidifies into a glass-like material without crystal formation. It is typically black in color and has a smooth, glassy texture due to its rapid cooling process.
Obsidian
Crystal size in these rock types is determined by their rate of cooling. Pegmatites have large crystals due to very slow cooling. Obsidian has microscopic crystals due to almost instantaneous cooling.
Obsidian cooled very quickly. It's a vulcanic glass, meaning that the crystals are so small, they had virtually no time to form an orderly crystalline texture, and are basically placed randomly. Smaller grain size is associated with faster cooling.
The black volcanic rock with small crystals is most likely basalt. Basalt is fine-grained and is commonly found in volcanic regions as a result of solidified lava flows. The small crystals are often composed of minerals such as plagioclase and pyroxene.
Obsidian cools rapidly, preventing large crystals from forming. As a result, the mineral crystals are too small to be seen with the naked eye. The rapid cooling process hinders the growth of crystals, resulting in a smooth and glassy texture.
Igneous rocks will have small crystals if they cool rapidly. This is because rapid cooling does not allow enough time for large crystals to form. Examples of igneous rocks that exhibit small crystals due to rapid cooling include basalt and obsidian.
Igneous rocks with very small or no visible crystals are formed by rapid cooling. A good example would be obsidian (which is a volcanic glass) and BAsalt which may have an aphanitic texture (crystals to small to see with the naked eye).
small scale grain production
The weight of obsidian is approximately 2.3 to 2.6 grams per cubic centimeter.
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