Hematite vs Obsidian: What Are They, And What’s The Difference?

Hematite and obsidian are two stones that sometimes are confused by rock enthusiasts who don’t know the differences to look out for between the two.

Thankfully, telling them apart doesn’t have to be difficult.

Here is everything you need to know about these two interesting stones.

Hematite vs Obsidian (EXPLAINED)

What Is Hematite?

Hematite is one of the most abundant minerals found both on the surface and within the shallow crust of the Earth.

It is an iron oxide, a common rock-forming mineral that can be found in many sedimentary, igneous, and metamorphic deposits.

Although once mined at thousands of locations, this important iron ore is mined today from a handful of large deposits, most notably in China, Australia, Brazil, and India. 

Hematite has a widely varying appearance, which is what often leads it to be confused with other stones.

The colors can be found in the range from red to bow and black to gray and silver.

However, regardless of the apparent color of the hematite sample, the streak it produces will always be reddish in color.

Checking for this red streak is one of the most reliable ways to test whether or not a sample is hematite or another mineral. 

While most samples of hematite aren’t magnetic, it is possible to encounter samples that have a high enough magnetite composition for them to be able to attract magnets.

Because of this, some hematite may be mistaken for magnetite or a weakly magnetic pyrrhotite sample.

However, a streak test will quickly clear up any confusion. 

In composition, most hematite is comprised of around 70% iron and 30% oxygen.

As with most other natural materials, it is rarely found in a pure form, and this is particularly true of hematite that forms via either organic or inorganic precipitation.

Clastic sediments can also add clay minerals to the iron oxide, which can create layered deposits of hematite and shale.

As a mineral, it can crystalize during the differentiation of magma or as precipitation from hydrothermal fluids moves through rocks.

However, hematite is most commonly found in sedimentary deposits created around 2.4 million years ago when the original oceans were iron-rich, but with very little oxygen.

As cyanobacteria evolved to become capable of photosynthesis, more oxygen started to fill the water, which combined with the iron to form hematite which then sank to the ocean floor, creating banded iron formations that we can encounter today. 

The layers of hematite at the ocean bottom are now hundreds to several thousands of feet thick in some places and together they form one of the largest rock formations on the planet. 

Hematite has been in use by humans for thousands of years, and it is one of the most important ores of iron.

The word hematite comes from the Greek word “haimatitis”, meaning “blood-red”, and it was called thus due to its bright red color when crushed into a fine powder.

When crushed into a powder, hematite has been used as both a paint and a cosmetic, and it is hematite pigments that were used to create some of the most common pictograph cave paintings that survive today. 

Fascinatingly, hematite isn’t unique to our planet, and it has in fact been discovered to be one of the most prevalent minerals on Mars.

It is these rocks, rich in iron, which help give the red planet its signature color. 

What Is Obsidian?

Obsidian is a mineraloid that is formed when molten material cools so rapidly that the atoms are unable to form into crystalline structures.

The result of this rapid cooling produces a smooth volcanic glass that has a uniform texture and a conchoidal fracture. 

Usually, an extrusive rock, meaning it solidifies above the Earth’s surface as opposed to below it, can be formed in a variety of environments that are conducive to rapid cooling.

These can include along the edges of a lava flow, around sills and dikes, along volcanic domes, where lava meets water, and when lava is thrown into the air.

It is most commonly black in color, although it can be green, brown, and tan.

Rarely can obsidian even be found in shades of yellow, orange, blue, and red.

These rarer colors are thought to be caused by inclusions and trace elements that give the obsidian a more unique coloration. 

Sometimes obsidian can also be found two have two colors swirled together.

Known as mahogany obsidian, this combination is usually black and brown. 

Some obsidian specimens have a composition that is relatively similar to granite and rhyolite, both of which can form from the same material as obsidian.

As a glass, obsidian is chemically unstable and some may begin to crystallize overtime at a rate that isn’t uniform throughout the specimen.

This localized crystallization results in what is known as snowflake obsidian, and it can display radial clusters of cristobalite crystals. 

Obsidian can be found throughout the world, although it is typically confined to areas of recent geological activity.

Rarely will obsidian be over a few million years old, as it is rapidly destroyed via weathering, heat, and other natural processes.

The largest deposits of obsidian can be found in Argentina, Chile, Ecuador, Guatemala, Iceland, Canada, Russia, Mexico, and the United States.

In the U.S., obsidian is only found west of the Mississippi as the east hasn’t experienced recent volcanic activity.

The states with the most obsidian are on the far west coast, such as Arizona, California, Nevada, New Mexico, Oregon, and Washington. 

Obsidian has been used by humans for thousands of years and was commonly fashioned into knives, arrow tips, and spear tips due to its sharpness.

Today, obsidian is still used for its sharpness, and in modern surgery, obsidian is used to create tools with a thinner and sharper edge than even the best surgical steel. 

See also: Can Black Obsidian Go In Water?

Hematite and Obsidian: Telling The Difference

When it comes to telling hematite and obsidian apart, there are a few key things to look for.

For example, hematite is far heavier than obsidian due to its high iron content.

Polished hematite will also have a metallic luster that isn’t common for obsidian.

If you touch the two, obsidian will feel much more like glass, while hematite will feel much more stone-like.

One of the best ways to tell is by conducting a streak test.

Obsidian will produce a white streak, while hematite will always have a rusty red streak that is unmistakable. 

Two Great Stones for Collecting

Both Hematite and obsidian make great inclusions to any rock enthusiast’s collection, and they both have interesting histories.

Now that you know how to tell the two apart, you can start looking for the best specimens to add to your personal collection.

hematite vs obsidian