If you're wondering about rocks that look like glass, you may or may not know why they have this appearance. In case you don't know why some rocks look like glass, take note. Such rocks have intriguing relationships with minerals and magma. Some glassy-looking rocks are more common than others, which is why a few of them are beautiful enough to gain popularity as gems.
Diamonds look a lot like glass, but they're much harder, and can effortlessly cut a hole into glass. Diamond rock formations don't occur easily. It takes a lot of high pressure and heat for a diamond to form from a mineral known as graphite. Most diamonds form from the graphite that sits nearly 100 miles below the Earth's surface. Magma carries them up where they can be found by diamond miners.
Emeralds are as clear as panes of window glass, but they're richly green in color. They're also far more durable than household glass. Emeralds form in response to the Earth's hydrothermal processes. Without rainwater or water from cooling magma bodies, emeralds would not form in the cracks of the Earth. Emeralds are precious because the precise conditions and metallic element that forms them, beryllium, are rare. Emeralds are one of six distinct gemstones within the beryl mineral family, and it's the most sought-after.
Aquamarine stones are fairly clear and may resemble beautiful pieces of old soda-pop glass. This beryl mineral is bluish-green, but may also form in pure-blue tones, which is this rock's most sought-after color. It's a hard rock, like the emerald and diamond. Emeralds gain assorted colors from iron-based impurities. The location of these impurities dictate which color an aquamarine rock becomes.