Polarised light micrograph of Lasa marble from the Goflaner marble quarry, Vinschgau, South Tyrol, Italy. This marble was formed 350-380 million years ago through the metamorphic transformation of very pure limestone that was originally deposited as marine sediment on the northern edge of the North African continental plate. The limestone was shifted to the Vinschgau area by plate tectonics and sunk into the Earth' mantle. The high pressure and heat turned the limestone into marble. Lasa marble is composed of 96.6 to 98.6 percent calcite and calcium carbonate, with quartz and apatite secondary components. Magnification: x60 when printed at 15 centimetres wide.