Obsidian is a natural volcanic glass formed when lava solidifies so quickly that mineral crystals do not have time to grow.

Obsidian is not crystalline and does not have a well-defined chemical composition. Therefore, it is said to be mineral-like but not a true mineral. Obsidian is at least 70% silicon dioxide.

According to Pliny the Elder of Rome, this substance was very similar to the stone found in Ethiopia by Obsidius, a Roman soldier. Hence, the root of the name Obsidian.

Obsidian is hard and brittle and it fractures with sharp edges. It is remarkably vitreous and is transparent to opaque. It has a hardness ranging from 5 - 5.5 on the Mohs scale.

Though obsidian is usually dark in color, the color varies depending on the trace elements or impurities present in it. It can come in a variety of colors including black, grey, brown, orange, striped, spotted, pink and in some rare cases, colorless, green, red and blue.

Obsidian is considered the stone of the Mayans and Aztecs. It has not only been fashioned into weapons such as knives, arrowheads and spears, but also it was used to make magical scrying mirrors and other sacred artifacts and ornamental jewelry.

The ancient Nahua speakers of Mesoamerica called obsidian “Itztli” which literally means Obsidian Knife.

In the religious text of the Mayans, the Popol-Vuh, we read that: “After playing well for awhile the twins allow themselves to lose, and they are given until the next day to come up with the flowers. This time they must spend the night in Razor House, which is full of voracious stone blades that are constantly looking for something to cut. In exchange for a promise that they will one day have the flesh of animals as their food, the blades stop moving.” (Taken from: 1550 POPOL VUH: THE MAYAN BOOK OF THE DAWN OF LIFE),

Not only Mesoamericans used obsidian in the production of sacred statues of their gods and heroes, the Greek and Romans did as well.

The Romans and Greeks were fond of fashioning camei and intagli out of obsidian.

Ancient Egyptians used obsidian blades to cut the bodies of their high priests and kings before the mummification process.

In the 18th century the term "obsidians" was used to refer to all antique pastes which were imitation gems made from glass. The Romans were very skillful in producing such colored glass pastes.

Obsidian is often confused with Moldavite, especially of the black Moldavite variety. However, Moldavite often occurs in olive-like or bottle-green color. Hence, it is also called Bottle Stone. Moldavite, like obsidian is a glass. But it is a tektite formed by a meteor strike whereas obsidian is a glass created from a volcanic eruption.

The non-volcanic origin of obsidian are the ones that are struck with lightning or volcanic rock dust that were heated. These are termed obsidianite. One such example is Helenite also known as Mount St. Helens obsidian, emerald obsidianite, and ruby obsidianite.

Obsidian is also confused with quartz. Quartz is 7 on the Mohs hardness scale whereas obsidian has a hardness ranging from 5 to 5.5.

Obsidian is of a single refraction, whereas quartz is of a double refraction.

Other gemstones that look similar to obsidian are Hematite, Aegirine-Augite, Gadolinite, Pyrolusite And Wolframite. They all have a higher density than Obsidian. Jet also looks similar to Obsidian. However, Jet has a Mohs hardness scale ranging between 2.5 and 4.

Pure obsidian comes in black color. This dark color in obsidian is due to the presence of iron and magnesium. However, there are other varieties of obsidian.

Colorless obsidian does exist, but is rare.

Mahogany obsidian is of a dark-brown to black and red banding.

Sheen Obsidian is dark-brown to black with a golden or silver sheen (or with aventurescence).

Rainbow Obsidian is dark-brown to black with an iridescent sheen. The iridescence of obsidian can be gold, silver, blue, violet, green, or a combination of these colors. The rainbow colors of Rainbow Obsidian are due to the presence of augitic pyroxene.

"Fire" or "flame" obsidian reflects bright colors due to the presence of nanometric magnetite crystal layers. Transparent pale yellow-green to brownish obsidian from Peru is referred to as Macusanite.

Translucent to opaque, black-streaked orange, red or brown obsidian nodules from the American Southwest are known as "Apache tears".

Orange obsidian is referred to as "pumpkin obsidian" and plum-colored obsidian is called "plum obsidian".

Other varieties of Obsidian include:

The Snowflake Obsidian and the rare Peanut Obsidian; the Midnight Lace Obsidian and the Cat's Eye Obsidian. The Cat's Eye Obsidian displays chatoyancy (or the cat's eye effect).

Some obsidian comes with inclusions which cause it to have a silver or golden sheen. These inclusions can be needle-like, gas bubbles, torpedo-shaped bubbles, teardrop-shaped bubbles or cristobalite crystal which appear like "snowflakes" in snowflake obsidian.

These bubble inclusions can produce interesting effects such as a golden or rainbow sheen.

Obsidian from Chile contain the very rare euhedral indialite crystals and transparent rods of sillimanite inclusions. Bolivian obsidian contains the orange spessartine inclusions.

As obsidian literally comes from the core of the earth, it vibrates a very high frequency. It is a powerful sacred stone that protects the wearer from any sickness and trouble.

Obsidian is called the Stone of Truth, because in ancient times it was the material used in fashioning scrying mirrors to discover occult secrets and truths.

These mirrors were also used to contact the spirit world and to look into the future as well as the past.

The sorcerer and astrologer of Queen Elizabeth, John Dee, used an Aztec scrying mirror to contact Angels. Today this mirror is on display at The British Museum.

Some of the pupil of the eyes of the Eastern island Moai statues are made from Obsidian.

A carnelian and gold shen amulet was found near the neck of Reniseneb's mummy along with a necklace of obsidian and gold.

In ancient Egypt, Obsidian were put on the body of the deceased in order to protect it in the afterlife.

Hindu chakra system posits obsidian at the root chakra.

Obsidian can produce cutting edges many times finer and sharper than even the best steel scalpels. It is so sharp that it cuts at a cellular level. It is even reported that it is able to cut an atom in half. Some surgeons still use obsidian blades as surgical scalpel especially in intricate procedures today.

Obsidian is found in places that have experienced volcanic eruptions. Such places include Argentina, Armenia, Azerbaijan, Canada, Chile, Georgia, Greece, El Salvador, Guatemala, Iceland, Italy, Japan, Kenya, Mexico, New Zealand, Peru, Scotland, Turkey and the United States.