Marble

hard quartzite rocks. They do not erode easily. They can crush shale and limestone if they lie above them, forming large escarpments along riverbeds.

Quartzite is quartz upon quartz, or basically quartz crystals that are cemented by other quartz molecules. There is also orthoquartzite, which is similar but has a different type of cementing agent. Paraquartzite is quartz grains sutured so securely that they fracture in unique ways – usually along the planes of the crystals. Quartzite is hard but fractures in ways that can be dangerous to the person trying to fracture it. Fuchsite quartz is green due to chromium in the quartz.

You might also see quartzite whenever sandstone-like rocks are cemented together with previously dissolved silica. These are not as hard as real quartzite and will break down into soils that are high in silica.

MARBLE

Marble is the result of limestone having had heat applied to it. Thermal contact during volcanic eruptions or other volcanic activity creates this marble. You can also get regional limestone dynamically as the calcium carbonate becomes calcite. You then get a new kind of mineral called calcium silicate and wollastonite. Wollastonite is a calcium silicate used to make paints, brake pads, and other things that depend on the bright color of this stone.

The chemical formula for marble is calcium carbonate or calcite. It has a variety of textures and can be fine or coarse-grained in nature. Look for some banding in certain pieces of marble. While this is recrystallized calcite, it also has other substances in it, including garnet, serpentine, and olivine, which leads to its interesting coloration at times.

Chalk and dolomites will turn to marble as well but you won't see as many of these. All types of marble resist erosion and are used for a variety of major building projects and statues. The Taj Mahal is made almost entirely of marble.