Iâve come across a historical footnote on the English language and I thought everyone would get a kick out of it. Up until about 2 hundred years ago, there was a 27th letter in the English language. This letter is still in common use today and I would bet that you have used it recently. But this letter is no longer considered a letter; it is now regarded either an abbreviation or punctuation. Iâm talking about the (&) ampersand.
Gneiss is a medium to coarse-grained, irregularly banded rock with only poorly developed cleavage. The light and dark bands (gneissic banding) are alternations of felsic vs. mafic layers. Slate is a product of low grade metamorphism (not terribly great burial temperatures and pressures are required).
The smallest grains are called clay, then silt, then sand. Grains larger that 2 millimeters are called pebbles. Shale is a rock made mostly of clay, siltstone is made up of silt-sized grains, sandstone is made of sand-sized clasts, and conglomerate is made of pebbles surrounded by a matrix of sand or mud.