Smooth Blue Amber; Dominican Republic: "The color is a result of blue fluorescence and no solid blue color. The color may be a result of volcanic dust or ash present when the resin was pressed out millions of years ago."
Iceland spar is a clear, transparent, colorless crystallized variety of calcite (calcium carbonate, CaCO3). Large pieces are split along natural cleavage planes to form natural rhombs. Iceland spar is probably best known for exhibiting the optical property of double refraction – so, anything viewed through the crystal appears double. It has many uses, in everything from precision optical instruments to LCD screens, and was even used during WWII to make bombsights.