Origins and Formations, Part II

Okay, back again tonight to discuss an essential subject: How gemstones are formed. All gems that have a mineral origin are found in rocks, or "gem gravels" that come from those rocks. As you may or may not remember from middle school Earth Science classes, all rocks are made up of one or more minerals and can basically be divided into three main "types". The formation of these types, by name igneous, sedimentary, or metamorphic, is a continuous process. The term "rock cycle" is used to describe this process. Take a look below at the chart so you can get a better idea of what that process includes: 

The Rock Cycle

 Gem-quality minerals within these rocks can sometimes be easily accessible at the surface of the Earth, or they can be buried deep beneath it. The ones separated from their host rock by the process of erosion are carried through rivers out to lakes or the sea. 

Now Let's go through the different varieties of rocks. Although a little on the tedious side, this information is crucial to understanding gemstone formation and, later on, gemstones themselves. Igneous Rocks: These rocks have solidified from molten rock from deep beneath the Earth's surface. Some of these, called extrusive igneous rocks, are thrown from volcanoes in the form of lava, volcanic bombs and ash. Intrusive igneous rocks are ones that solidify beneath the surface. Here's the essential idea: The slower a rock cools and solidifies, the larger the crystals... and the gemstones inside those crystals. Many of the larger gemstone crystals out there form in pegmatite, a form of intrusive igneous rock. Metamorphic Rocks: These rocks are either igneous or sedimentary rocks, changed by the heat and pressure from inside the Earth, forming new rocks with new minerals. When this happens, sometimes gemstones can grow inside of them. Take Garnets for example. They can form within micha schists, rocks which were once mudstone and clays. And Marble can contain rubies because it's formed from limestone that has been under crazy heat and pressure. Sedimentary Rocks: These are formed by the accumulation of rock fragments made by the process of weathering. After a time, the fragments settle and harden into rock again. These rocks are usually laid down in layers, and these layers are sometimes treasured as a feature in decorative stones. Look at Australian Opal. It occurs in sedimentary rocks. Turquoise occurs as veins in rocks such as shale, and halite and gypsum are both sedimentary. Organic Gems: These, as we've talked about before, come from plants and animals. Pearls, as most people know, form around foreign bodies that made their way into marine or freshwater shellfish. Cultured pearls, on the other hand, are created artificially in big fisheries, usually in shallow waters like the ones off the coasts of China and Japan. Shells can be treated as gems too, and can come from different creatures like snails, turtles, and animals ranging from the ocean to freshwater to land. Like coral for example. It's made from the skeletons of coral polyps, tiny little marine animals. And think about bone, or ivory from the teeth or tusks of mammals. They can come from living animals, or from fossils that are thousands of years old. Then there's Amber, which is fossilized tree resin. You can collect it from soft sediments or straight from the sea. Finally, Jet is fossilized wood, found in certain sedimentary rocks.

Igneous Rock

Metamorphic Rock

Sedimentary Rock

Amber - Example of Organic Gem

Well, that's enough for one post! Hopefully I kept it as light a fare as possible for you all. Next we'll be discussing basic gemstone locations, and from there physical properties. Until next time, and thanks for reading!