No. One seldom finds obsidian in a coal mine.
Anthracite.
Glass is comprised of silica, which makes up approximately 15% of our planet. Glass occurs naturally wherever silica is heated to very high temperatures, such as a creator. Glass can be produced naturally, but the glass used today is manufactured the same way mother nature would. Heating silica until it melts, and allowing it to cool. The only difference is, people give it shapes that are not naturally found. Glass can be found naturally found in Obsidian. Found near lava different materials melt and form Obsidian
Obsidian, or "volcanic glass," is made when molten rock comes out of a volcano and cools so quickly that no crystalline structure has time to form. This makes obsidian an extrusive igneous rock. The cooling occurs right at the surface.
Anthracite forms from the metamorphism of bituminous coal. The metamorphism occurs due to pressures and temperatures from depth of burial or stresses derived from plate movements.
Obsidian, the rock that occurs when lava and water mix.
Obsidian
Obsidian is an extrusive rock that is a naturally occurring volcanic glass. It occurs when lava extrudes from a quickly cooling volcano, causing little crystal growth.
it occurs naturally
yes
Obsidian is volcanic glass that is formed naturally and found in certain parts of the world. It can be "chipped" like flint into arrow points and other shapes and when chipped it has extremely sharp edges. A few tribes certainly made their arrowheads of obsidian, but it was not widely available; in his 1989 study of "Bows and Arrows of the Native Americans", Jim Hamm lists the types of points used in the area that became the USA; obsidian only occurs in the Great Basin of the south-west and on the west coast. It was also used by the Aztecs and other Mexican tribes. See links below for images:
it occurs naturally in grapes, bananas and tamarinds
The process through which anthracite coal is formed from bituminous coal is called coalification. This transformation occurs as a result of increased pressure, temperature, and time acting on the organic materials in the coal over millions of years, leading to a higher carbon content and a more compact structure in the anthracite coal.