Difference Between Gneiss and Limestone
Gneiss is a large group of metamorphic rocks, ie they are formed by other rocks that have been subjected to high pressures and high temperatures. Under these conditions the rocks were deformed and had a look that is often quite different from the outset. The starting point can be both sedimentary (eg sandstone) and igneous rocks (eg granite), which have in common that they have a high content of minerals quartz and feldspar. Beyond this gneiss a very diverse group of rocks, both in terms of color, to the structures found in them and the mineral content.
Limestone, on the other hand is a sedimentary rock, formed by the shells and plankton where calcareous skeletons have been deposited, or that coral reefs that have been accumulating on the seabed. As with all other rocks the limestone undergoes metamorphosis when exposed to high pressure and high temperature. Marble is a metamorphic limestone.
Sometimes gneiss is what we call a band appearance, ie it consists of “layers” with slightly different color and composition.
There are areas where the sandstone, shale (petrified clay) and limestone occur in the exchange. Sedimentary layers are formed by layers of clay, sand, gravel or limestone, when deposited in oceans, rivers and lakes. Gneiss is however a result of deformation of several kilometers deep below the earth’s surface. At great depths in the earth’s crustal rocks there is a tendency to behave like sticky dough. If one adds movement to this sticky dough (as for example when two continents collide and form mountain ranges), the “dough” of slightly different composition to crunches up and tangled in each other until one ends up with a gneiss.
When it comes to separating gneiss from the limestone, we should assume the hardness of the rocks. As mentioned, gneiss consists mostly of quartz and feldspar. These minerals are much harder than calcite, which is the dominant mineral in limestone. A relatively safe way to distinguish the two will therefore be to check the hardness of the rock. This can be done by scratch / pick at the rock with a steel object such as a pocket knife. The limestone will be scratched very easily, but the gneiss, it would be virtually impossible to scratch it. Another sure way to detect calcium stones is that they sometimes contain visible fossils, such as corals and shells.