Obsidian is an extrusive rock that erupted out of a volcano. Most volcanic rocks are rough and jagged because they contain gas bubbles. But obsidian is smooth because it contains mostly of glass.
Is obsidian coarse or fine grained?
The coarse-grained textures indicate intrusive rocks whereas the fine-grained textures generally indicate extrusive rocks. Extrusive rocks defined mainly by texture are discussed under rock textures: obsidian, scoria, pumice, tuff, and volcanic breccia.
Does obsidian have a glassy texture?
obsidian, igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Obsidian is extremely rich in silica (about 65 to 80 percent), is low in water, and has a chemical composition similar to rhyolite. Obsidian has a glassy lustre and is slightly harder than window glass.
What is the hardness of obsidian?
Because obsidian is not comprised of mineral crystals, technically obsidian is not a true “rock.” It is really a congealed liquid with minor amounts of microscopic mineral crystals and rock impurities. Obsidian is relatively soft with a typical hardness of 5 to 5.5 on the mineral hardness scale.
Is obsidian a strong material?
But while real obsidian looks like it’s also a deep, opaque black, if you hold it to the light you’ll usually see it shine with a green glow. That’s because obsidian is glass, and rather than being super tough, it’s brittle, shattering easily.
What does obsidian feel like?
True Obsidian will have a shiny glassy appearance and will feel smooth to the touch. It’s a natural glass so will have similar properties to glass although it will feel slightly harder and may have sharper edges.
Why is obsidian glassy?
Obsidian is a glassy igneous rock that usually forms as an extrusive, fast-flowing lava. When the lava cools so rapidly that atoms can’t form into a crystalline structure, this glassy rock is the result. It has a smooth, uniform texture and can come in many different colors.
What is characteristics of obsidian?
Obsidian is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. It is hard, brittle, and amorphous; it, therefore, fractures with sharp edges.
Is obsidian coarse?
Fine grained rocks, where the individual grains are too small to see, are called aphanitic. Basalt is an example. The most common glassy rock is obsidian.
Why does obsidian have a fine grain texture?
Very quickly cooled lavas, typically those quenched in water, will have a glassy texture. They cool too quickly to form crystals. Glasses do not have an orderly arrangement of atoms and there are therefore no minerals, in the strict sense, in them. Volcanic glass is called obsidian.
Is obsidian extrusive or intrusive?
Obsidian is an “extrusive” rock, which means it is made from magma that erupted out of a volcano. If it was an igneous rock that formed from magma underground and did not erupt, it would have been called an “intrusive” rock.
What is glassy texture in geology?
If a rock looks like a block of (colored) glass, with no visible mineral crystals, it has a glassy texture. Superficially, a glassy texture suggests cooling that was so extremely fast that no crystals could form.
Can obsidian be gray?
Usually black, obsidian can also be red or gray, streaked and mottled, and even clear.
Does obsidian have cleavage?
The obsidian exhibits a pronounced vitreous lustre. It does not scratch glass, thus corresponding to the hardness of 5 or 6 in the Mohs scale. It is translucent in thin cleavage fragments and along sharp margins.
What is obsidian density?
The density of obsidian is 2.55 g/cubic cm. It means it is heavier than water and dense medium as a mass.
Is obsidian heavy?
Obsidian is as heavy as any other average stone, since it is quartz, so if it is light weight, it is not obsidian.
