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National Old Rock Day

Collections of old rocks are brought out and polished up today because it's National Old Rock Day! Most rocks are quite old by nature, so pretty much all rocks are covered in today's celebration. Rocks are made up of solid crystals of various minerals or mineraloids, or of fragments of other rocks that have been fused and bound together into a solid. Large quantities of rock can be found under the soil and at the bottoms of the oceans, and rocks make up the foundation of hills, plains, mountains, and valleys.

The studying of rocks is known as petrology, and the process of their description and classification is petrography. Rocks fall into three categories: igneous, sedimentary, and metamorphic. Igneous rocks are volcanic rocks that are formed from molten material—either from lava on the Earth's crust or magma that has solidified underground—that has cooled and crystallized. Granite is one example of igneous rock that forms underground. A large portion of the continents are formed from granite, and some granite is believed to be billions of years old. The most common igneous rock is basalt, which is formed from dark lava of the same name. The seafloor is formed of basalt.

The second type of rock is sedimentary rock, which is made from eroded fragments and particles of other rocks, as well as from plant and animal remains. The particles are deposited in low areas like ocean floors, lake and stream beds, and deserts, and are compressed and compacted back into rocks there, where they are found in layers called strata. As animal remains may make up sedimentary rocks, fossils are often found in them. One example of sedimentary rock is sandstone, which is formed from sand, mudstone, and limestone.

The third type of rock is metamorphic rock, which is made from sedimentary or igneous rocks that have been transformed by heat, pressure, or an intrusion of fluids, in a process that is known as metamorphism, where the mineralogy in the rock changes. Some examples of metamorphic rock include marble, which is metamorphosed limestone, quartzite, which is metamorphosed sandstone, and gneiss, which can be made from both sedimentary and igneous rocks like granite and sandstone.

How to Observe National Old Rock Day

Some ways to spend National Old Rock Day include:

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