Granite is an igneous rock, and it was formed deep under the earth as hot molten rock cooled very slowly. During the cooling process, minerals like feldspar and quartz crystallized and bonded together. Because of the way it was formed, granite is very strong, and resists water and food acids. It looks like a bunch of crystals packed together very tightly. Some granites have larger crystals, and some have very small crystals. Granite is an extremely common stone all over the world. It is found on all seven continents. And the presence of different minerals during its formation causes granite to take on an almost endless variety of colors, from white to black, red to blue, and every blend of color possible.
Marble is a metamorphic rock. It began its journey as a coral reef beneath an ancient sea millions of years ago. The reef eventually became buried under earth and rock, and the calcium-rich bones of the little creatures which lived in the reef became calcium carbonate, or limestone. Then, the limestone was buried even further beneath the earth's surface, and, under heat and pressure, the calcium carbonate crystallized into marble. Marble is also very commonly found almost everywhere on earth. Because it is composed of calcium carbonate, it is easily soluble in food acids, and semi-soluble in water. Marble comes in almost as many colors as granite, and comes in a much wider range of patterns.