Onyx: This is what most geologists would refer to as banded calcite. Onyx is not unlike agate and is considered a “soft” stone. Calcite is the same mineral that makes up limestone, marble and travertine. As with travertine Onyx is formed literally on the surface as its formation comes from spring water or ground water that has an abundance of calcite dissolved in it. As this water either bubbles or cascades or softly emerges out of the spring the minerals precipitate out and form a crust of calcite crystals. With time, as the water continues to flow and more minerals settle the variations in the layers begin to form. The rate of flow of the water and other impurities assist in creating many of the variations in the layers. The most common colour found in the onyx is the rich honey colour caused by iron oxide. One can find beautiful layers of crystal in Caves or anywhere where there is underground water with mineral deposits.