Aquamarine is a type of beryl mineral and is formed in an igneous rock formation called a pegmatite. Wow, that is too many geological terms, let me try and explain each one (with the help of far more knowledgeable sources) so by the end of the article we all know how aquamarine is formed.
THE ROCK CYCLE On earth there are three categories of rock - sedimentary, metamorphic and igneous. Over many millions of years continual geological processes transform one type of rock into another. For our discussion we are interested in igneous rock.
Deep in the earth's core there is molten rock (magma) at extremely high temperatures. During volcanic events this magma is forced to the earth's surface and cools to form igneous rock. There are many different types of igneous rock depending on the processes and chemicals that form them; one of these is pegmatite.
PEGMATITE As the magma cools and solidifies, water that is trapped does not readily dissolve into the magma and becomes concentrated in cavities. These pockets eventually crystallize to form a special type of rock called a pegmatite.
Due to the high water content these crystals can form faster than other crystals, are often flawless and are usually quite large.
BERYL One of the minerals that can occur in these pegmatites is beryl and when certain other elements are present, different types of beryl are formed. The 6 main varieties of beryl are aquamarine (blue-green), emerald (green), morganite (pink), red beryl (red), heliodor (yellow) and maxixe (deep blue).
See the video of a miner finding an aquamarine crystal in Georgia, you can just imagine a pool of water trapped in the rock in ancient times and slowly forming this beautiful crystal. Notice the hexagonal (6-sided) shape and blunt ends which are characteristic of beryl.
So that is how aquamarine is formed - isn't it fascinating? High quality crystals are then cut into gemstones and set into the jewelry that we see in the stores, involving many skilled craftsmen along the way. So now hopefully when you read the first sentence again, it makes some sense! 🙂