Most Calcite is white or colorless, but impurities or inclusions produce different color shades. The admixture of manganese, iron, lead, copper, etc. produces yellowish tones, light blue, black, pink, brown, green, and gray colors. Bright pink calcite crystals colored by cobalt are probably the rarest. After quartz, calcite is the most common mineral found in the Earth's crust. The limestone variety of calcite forms whole mountain ranges, and has been used since ancient times in constructing marble temples, palaces and sculptures. Crystallized calcite had no practical application for centuries until the discovery of large transparent crystals near Helgustadire, Iceland which enabled the Danish physician Erasmus Bartolinus, in 1669, to study for the first time the birefringence of light. Clear crystals, called Iceland spar, give marked double refraction and are used in polarizing microscopes. Fine calcite crystals are found in many localities worldwide, but especially at Malmberget, Sweden.