Facts about Rocks
- 10
Mohs hardness scale, created in 1812 by mineralogist Friedrich Mohs, rates rocks and minerals from 1 to 10 based on scratch resistance, with talc at the softest and diamond at the hardest.
- 09
Feldspar minerals comprise approximately 60% of Earth's continental crust and weather into clay minerals that form the basis of soil supporting all terrestrial plant life.
- 08
Stalactites and stalagmites grow at rates between 0.3 and 3 millimeters per year in limestone caves as mineral-rich water deposits calcium carbonate layer by layer.
- 07
Marble, a metamorphic rock formed from limestone under intense heat and pressure, can be dated to 2.5 billion years ago in the Isua Greenstone Belt of Greenland.
- 06
Basalt, the most abundant rock type in Earth's crust, comprises approximately 90% of all oceanic floor and erupts at temperatures around 1,200 degrees Celsius from mid-ocean ridges.
- 05
Diamonds form in the Earth's mantle at depths exceeding 120 kilometers where pressures reach 50,000 times atmospheric pressure, requiring temperatures above 1,200 degrees Celsius.
- 04
Pumice, a volcanic rock so porous it can float on water for years, was discovered drifting across the Pacific Ocean in 2012 from an underwater eruption near Tonga.
- 03
Granite takes approximately 10,000 to 30,000 years to cool completely from molten magma into solid crystalline rock deep within the Earth's crust.
- 02
Obsidian, a volcanic glass formed from rapid cooling of lava, can be fractured to create edges sharper than surgical steel at approximately 3 nanometers thick.
- 01
The oldest rocks on Earth, found in the Jack Hills of Western Australia, are zircon crystals dated to 4.4 billion years old.