The name is derived from the German "quarz" of uncertain origin. It was called "krystallos" by the Greeks, but this later became the generic term for crystal.
Petrified wood (fossilized wood to be politically correct) is created when a tree is buried in sand and slowly replaced by a silica solution over a few million years. Again the color is caused by the secondary elements found in the solution.
These stones cut by the author. The top stone is petrified palm wood and the bottom one is petrified sycamore wood. This particular piece of fossil wood even has what the woodworkers call "feathers".
Palm slab closeup
Palm slab closeup II
Sycamore slab closeup - notice even the bark on the exteriror.