Is it worth more at higher weights.
Right, iceland spar is calcite. It is much softer than quartz and will not scratch glass, but quartz will. A steel knife will scratch calcite but not quartz. The paper will tell you it is calcite if you draw a line on the paper and when you put the sample on top of it you see two lines.
Iceland spar is calcite and it bends the light so you see a double line. micro.magnet.fsu.edu/optics/light...
