Want this question answered?
Ther is no set answer to this question. Each opal is unique and has its own value. From colorless opal to the most prized fire opal it depends on the size and color. A good place to get the idea of the value of opal is to go to ebay and type in opals. You will see prices from a few dollars to over 50,000 dollars.
From the size of a grain of sand, to about the size of a grain of rice. A meteor the size of e kernel of corn would be rare. Bigger ones do come along, but things the size of a baseball probably only hit the Earth once a week or so.
they are about the size of a grain of sand.
1 Micrometer across
If the sun were the size of a human eyeball then Earth would be the size of a grain of fine sand.
Grain size increases in the process of recrystallization.
It depends on if it is intrusive or extrusive. If it is an intrusive rock, it is formed when magma hardens under the earth and has a larger grain size. If it is an extrusive rock, it is formed when lava hardens on the earth's surface and has a smaller grain size.
Grain refers to particle or crystal size in rock.
1.Grain Size 2.Grain Shape 3.Grain Pattern
Grain size and arrangement.
The cooling rate of the rock.
the size of a sand grain or smaller
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.
The name of a rock is usually derived from the sediment grain size.