According to National Geographic, the main difference between rocks and stones, or gemstones, are their rarity and crystal formation. Most gemstones have a crystal formation, which makes them rare and valuable after they are cut. Rocks usually do not have a crystal formation, which means they are not considered to be of value. Unlike rocks, gemstones are classified on their rarity and value into two categories: semiprecious and precious.Continue Reading
Both rocks and gemstones are made of the same substances, minerals. However, rocks contribute to the formation of landforms and natural resources such as tin, iron, gold, granite and marble. Gemstones, on the other hand, are mostly prized for their beauty even though when uncut they appear to be ordinary rocks. However, another reason why gemstones are considered precious is because there are fewer gemstones available; also, the process used to find gemstones is very challenging and often requires a workforce. Diamonds, rubies, emeralds and sapphires are all considered to be precious gemstones.
Generally, rocks and gemstones are formed under similar conditions. However, the formation of some stones is due to the location of its formation in the Earth’s crust. For the most part, gemstones are formed below the Earth’s surface and are brought to the surface by mining; this is not often the case for rocks. A diamond, the most precious gemstone, is made from carbon and formed under extreme pressure at least 100 miles under the Earth’s crust. It is the hardest natural substance found on the Earth. Graphite, a rock, which also is made from carbon, is formed on the Earth’s surface. Because it is formed closer to the Earth’s surface without extreme pressure, it forms into a soft rock instead of a diamond. It is the one of the softest rocks on the planet, which is one of the reasons why it is used effectively as pencil lead.Learn more about Geology
Porphyritic rock is a texture of igneous rock with two distinctly different crystal sizes due to two periods of cooling occurring at different rates. Larger crystals are called phenocrysts, while the smaller grains are known as groundmass or matrix.Full Answer >
The principle of superposition in geology states that rock forms horizontally, with the oldest layers of rock lying at the bottom of a formation and newer rock resting on top. For instance, the Kaibab Limestone at the edge of the Grand Canyon is younger than the Toroweap Formation below it.Full Answer >
Wind and rain erode rock to begin the formation of siltstone. The rock particles break down further as they travel with the water and then settle to the bottom of the water when it slows. Layers of silt accumulate, creating heat and pressure that cement the silt together into rock.Full Answer >
Water and ice cause weathering in rocks by causing bits of the rock to separate and flow away through the erosion process. While this process is extremely slow, it is also inexorable, and any stone object exposed to the elements disintegrates in this way.Full Answer >