Black obsidian is a stunning form of volcanic glass. Technically it is the product of quickly cooling lava formed at the edge of lava flows. It has a high silica content which makes is very sharp when fractured. This has made it a popular material for honing blades and cutting tools throughout human history. Today it is still used in scalpels, as decorative blades, in jewellery and as a gemstone in its own right.
Do you have an obsidian sample and want to tell if it is real obsidian or not? Perhaps you found a beautiful piece of obsidian jewellery or an ornamental knife and you are wondering whether it is genuine or not? Or you might just be a curious geology enthusiast? Well that makes two of us! Today we’ll take a closer look at exactly what obsidian is, its properties and characteristics. We’ll provide you with a guide, with comprehensive steps to help you tell real black obsidian apart from fake black obsidian.
What Is Black Obsidian?
Obsidian is an igneous rock which was formed on the edges of lava flows – rhyolitic lava flows, A.K.A. obsidian flows to be exact. It can also be found where these lava flows have reached a water body, like a lake or the sea, and contact with water has sped up the cooling process. It is formed from felsic lava – these flows are characteristically low temperature with relatively high viscosity due to a high silica content.
The edges of felsic lava flows cool very rapidly, forming obsidian and inhibiting the formation of a crystalline structure. This lack of crystals is a key characteristic of obsidian and gives it a distinctive, smooth, and glassy texture, hence the reason it is classed as a volcanic glass.
The smooth, homogeneous texture of obsidian means that when it fractures the edges of the fracture are incredibly sharp. If we want to get technical, the fractures are termed conchoidal. This describes materials which fracture in a smooth, rounded way, bearing a resemblance to a scallop shell. As a fairly soft rock, obsidian can be broken and scratched relatively easily.
Obsidian has a very high silica content, and is composed of between 65-80% silicon dioxide, SiO2. Usually obsidian is black because it contains the minerals magnetite and/or hematite. The presence of magnetite can make an obsidian sample slightly magnetic! Obsidian can sometimes be much paler and even appear translucent. Some samples carry tints of color depending on their component minerals. For example, the presence of iron can give a green tint.
The oldest samples of obsidian that have been found so far date back to the Cretaceous Period. This is because obsidian is metastable when located on the surface of the Earth – over time it begins to break down into individual mineral crystals due to natural weathering processes.
What Is Obsidian Used For?
Due to the dangerously sharp fracture lines obsidian possesses, it has been used since pre-historical times for blades and cutting tools. The relatively soft quality of this rock means its edges can be easily honed and this is the reason why it is still used today in scalpels. Some claim it does a better job than modern steel scalpels.
Samples of obsidian used as mirrors and decorative objects have also been found throughout human history, particularly by the Aztecs and Ancient Greeks. In fact, there are some locations that are suspected of having been obsidian ‘manufacturing’ sites. Piles of obsidian chips have been found – an indication that ancient people processed obsidian tools and weapons on a relatively large scale in one location, an ancient factory!
How To Tell If Obsidian Is Real: 7 Steps
So, if you’ve got something you suspect is black obsidian but you want to be 100% certain, there are ways you can identify whether it is real obsidian. Take these easy steps and satisfy your curiosity:
1. Surface Texture And Appearance
Black obsidian has a distinctively glassy, smooth texture. It is often described as having an appearance like a frozen liquid. When a sample has been polished, the surface can be very shiny and reflective. When newly broken, obsidian fractures also have a shiny luster.
2. Type Of Object
Obsidian is relatively soft (more on this in step 6) which limits its durability for use as jewellery. Therefore it is only usually used for pendants, brooches and earrings. It can’t be used for objects like bracelets and rings which get a lot of wear as it can be chipped and scratched quite easily.
True obsidian will feel dense and heavy compared to common, fake obsidian materials like glass. Hold it in you hand and weigh it against a piece of glass of roughly the same size if you can find it. Does it feel heavier? Does it have a denser appearance.
As volcanic glass, obsidian can often be translucent. Try holding your piece up against a light to see whether it is translucent or opaque.
If you have newly shopped your piece of black obsidian, the price can be a good indicator of how genuine it is. The price will depend on the size of the piece, the quality (i.e. carat) and the processes it has been through. Small, unprocessed pieces of obsidian are sold for around $5-10 USD, while larger, processed pieces can fetch hundreds of dollars. Although black obsidian is not the most expensive gemstone, it is comparatively rare due to the ease with which it breaks down via weathering processes.
6. Hardness And Fracture
Obsidian has a hardness of between 5 and 6 on the Mohs hardness scale. This means you can test whether it can be scratched by common household objects or not. First, try scratching it with your fingernail. If it doesn’t scratch, try a penny. If that doesn’t leave a mark, try scratching it with a kitchen knife. Obsidian should be able to be scratched by a kitchen knife and any objects classed as harder than a kitchen knife including a steel nail.
If you can risk sacrificing a part of your obsidian piece, you can try to break it to inspect the fracture – but please do so with care! Obsidian breaks relatively easily, and is described as being stronger than window glass. The fracture lines should be curved and rounded, conchoidal like a scallop shell. The fractured edges will be very sharp so it is recommended to break the piece on a cloth with a hard surface behind, and to take care to clean up any stray fragments afterwards.
7. Ask A Professional With A Microscope
If all else fails, try to locate a professional geologist, gemstone expert or jewellery maker. Professionals with the right equipment should easily be able to tell real obsidian from fake. The use of a microscope will highlight the detailed structure of an obsidian sample, and a professional will look for giveaway characteristics and tell you for certain whether you have genuine obsidian or not.
Some commonly asked questions include how you can tell the difference between black obsidian and other black gemstones. Let’s look at the difference between some common lookalikes here. We’ll also answer some other questions relating to the use and properties of black obsidian, and where it can be found.
How can you tell the difference between black onyx and black obsidian?
These gemstones can look very similar to the untrained eye. They are both dense, black materials and can be polished to a high shine. The easiest indicator is weight – onyx is much heavier and denser than obsidian. It is also harder (around 7 on the Mohs scale of hardness), so you can try the scratch test. If it scratches with a kitchen knife it is obsidian rather than onyx.
How can you tell the difference between black obsidian and tourmaline?
Obsidian fractures in the distinctive, scallop shell-shaped fracture lines while tourmaline does not. It is also much smoother than tourmaline which is rough and lumpy.
How can you tell the difference between black glass and black obsidian?
This is perhaps the trickiest one – black glass can look and behave very similarly to black obsidian and this is why it is commonly sold as fake obsidian. Because obsidian is volcanic glass, it fractures in a very similar way, and has similar translucent, smooth and shiny qualities. However, glass cannot be honed in the same way i.e. the fracture cannot be sharpened to form a sharp blade. Black glass also tends to be more translucent than black obsidian. And black obsidian tends to be harder then glass, so potentially harder to break. These are not hard and fast rules though and a professional should be consulted if you suspect your obsidian is glass.
Where In The World Can You Find Obsidian?
Generally, obsidian can be found wherever there is volcanic activity and there have been lava flows in the past. Some locations with a significant obsidian deposit include Iceland, Russia, Japan, Kenya, Canada, Mexico, Chile and the US. If you live in the US and you’re keen to check out some obsidian ‘in the wild’, Glass Butte in central Oregon is the best place to take a field trip. (Check out these other obsidian-rich US locations here!).
If you want to collect obsidian you should check the local regulations first. In some areas it is prohibited to take obsidian from a natural deposit.
What properties does black obsidian have as a gemstone or crystal?
Some people believe obsidian can be used for protection, and to cleanse your home. It may be used to shield a person against negative energy. Many people have black obsidian crystals, palm stones, carved objects and more, and like to keep them around the house or on their person as a protection stone.