Marble, formed from limestone with heat and pressure over years in the earth's crust. These pressure or forces cause the limestone to change in texture and makeup. The process is called recrystallization. Fossilized materials in the limestone, along with its original carbonate minerals, recrystallize and form large, coarse grains of calcite. Impurities present in the limestone during the recrystallization period affect the mineral composition of the marble which is formed. At relatively low temperatures, silica impurities in the carbonate minerals form masses of chert or crystals of quartz.
At higher temperatures, the silica reacts with the carbonates to produce diopside and forsterite. At a very high temperatures, rarer calcium minerals, such as larnite, monticellite, and rankinite, forms in the marble. If water is present, serpentine, talc, and certain other hydrous minerals may be produced.
The presence of iron, alumina, and silica may result in the formation of hematite and magnetite. Marble does not split easily into sheets of equal size and must be mined with care. The rock may shatter if explosives are used. Blocks of marble are mined with channeling machines, which cut grooves and holes in the rock. Miners outline a block of marble with rows of grooves and holes. They then drive wedges into the openings and separate the block from the surrounding rock. The blocks are cut with saws to the desired shape and size.