obsidian doesnt crystalize because it was formed under water.
obsidian
Obsidian forms when lava cools very quickly, preventing the formation of crystals. This rapid cooling doesn't allow enough time for the minerals in the lava to organize into a crystal lattice structure, resulting in a glassy texture instead.
Glassy rocks are rocks that have cooled and solidified quickly, without forming crystals. This rapid cooling prevents mineral crystals from growing, resulting in a smooth and glass-like texture. Obsidian and pumice are examples of glassy rocks.
Obsidian rocks are cooled very fast, and you cannot see the crystals in them.
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 is an extrusive rock and is formed from rapidly cooling magma. Obsidian is also known as volcanic glass and one can find only sub-microscopic crystals in it. This is because it was cooled too fastly for large crystals to form. If the material that obsidian consists of were an intrusive rock and had a lot of time to cool down, one would find that it would be composed of easily visible crystals.
Obsidian are volcanic Glasses that cool very rapidly. The crystals are not allow to arrange them self's that is why Obsidian has not 3d internal structure. The are Igneous Glasses
Granite is a coarse grained igneous rock without Pyroxene.
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.
The texture of a rock depends on the rate that it cools. Obsidian cools so quickly that no crystals can form, therefore giving it a glassy texture.
Obsidian lacks crystals because it is a type of volcanic glass that cools too quickly for mineral crystals to form. Pumice and scoria lack crystals due to their porous nature and high gas content, preventing the growth of crystalline structures during cooling.
They cool to quickly for crystals to form.