What is a 'touchstone"?

1 ⤊

What is a 'touchstone"?

I thinks it has something to do with metal and is a kind of rock.

2006-10-30 08:02:26 · 1 answers · asked by Diana P 3 in Science & Mathematics ➔ Earth Sciences & Geology

1 answers

A touchstone is a small tablet of dark stone such as fieldstone, slate or lydite, used for probing of precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace.

By rubbing the metal on a touchstone a small amount of metal is ground off onto the stone, and forms a colored stripe. This is typically compared to a stripe ground from an alloy of known high-quality composition next to the sample.

2006-10-30 08:05:30 · answer #1 · answered by Leah H 2 · 1⤊ 0⤋