Why chalcopyrite is sometimes called fool gold

However, they can be distinguished by their shapes and crystal habits. Pyrite is a hard mineral with Mohs hardness of 6 to 6. Its crystal system is isometric with larger crystal occurs in extremely well-crystallized shape of cubes, octahedrons and pyritohedrons dodecahedral.

The smaller Pyrite crystal aggregates usually display a stunning glistening effect in light which occur grainy, encrusting and fibrous. The most distinctive characteristic of Pyrite crystals is its striated faces. Chalcopyrite is a relatively soft mineral, the hardness varies between 3. Chalcopyrite crystallizes in the tetragonal system and often occur as groups of small, distorted crystals in a globular or botryoidal shape.

It can be distinguished from Pyrite due to its iridescent tarnish appearance and a greenish black streak in its finely powdered form. They are often scattered in clusters or powder over the surface of a host crystal like Calcite and Fluorite, see the below two gorgeous specimens :D. Chalcopyrite on Fluorite and Calcite. Chalcopyrite on Calcite. Surprise, surprise!

All Posts. Gold crystals do not have striations. E Specific Gravity: Gold has a specific gravity of about The specific gravity of pyrite is about 5. All gold found in nature is always alloyed with other metals. These metals have a specific gravity which will reduce the specific gravity of the specimen, but never enough that it approaches the specific gravity of pyrite. Specimens containing a significant amount of gold will always have at least two to three times the specific gravity of pyrite.

Gold's Streak: A copper penny and a tiny gold nugget on a black streak plate, with a small streak made by the nugget. The copper penny is in the photo to serve as a scale. The tiny nugget weighs 0.

A Streak: Gold has a yellow streak. Pyrite has a greenish black streak. Learn how to do the streak test here. B Hardness: Gold has a Mohs hardness of 2. Gold will not scratch a copper surface Mohs hardness of 3 , but pyrite will easily scratch copper. Gold can be scratched by a sharp piece of copper, but copper will scratch very few other materials. Learn about the Mohs hardness test here. C Ductility: Gold is very ductile, and a tiny piece of gold will bend or dent with pressure from a pin or a pointed piece of wood.

Tiny pieces of pyrite will break or resist the pressure. D Sectility: Small particles of gold can be cut with a sharp pocket knife. Small particles of pyrite cannot be cut. Chalcopyrite in Dolomite and Quartz: Gold-colored minerals can be tested even if they are embedded in a rock.

The gold-colored mineral in this rock is chalcopyrite, and a person could determine that it is not gold by poking the gold-colored material with a pin and observing if it dents or breaks. Click to enlarge. Chalcopyrite and small pieces of biotite or phlogopite mica can fool you. Chalcopyrite a copper iron sulfide has very similar properties to pyrite. It has a lower hardness than pyrite 3. If you intend to deal with gold in the future, it is a good idea to acquire some samples of both gold and pyrite and try out some of the tests listed below.

Gold has a remarkable ability to form crystal-like shapes, and those pieces of gold have a significantly higher value than the actual weight of the gold piece. We recommend abstaining from performing destructive tests on those gold pieces.

Non-destructive testing methods will not damage gold or pyrite and are often the simplest to execute. Tarnish, or patina is a thin layer of corrosion that forms on some metals and minerals.

It is usually a different color from the original mineral or metal and acts as a protective layer for the metal or mineral from outside elements. Pyrite, in the majority of cases, comes with tarnish on the surface of the mineral.

On the other hand, gold nuggets do not have tarnish and are quite bright, a defining characteristic of gold and one of the primary reasons why jewelry and decorations are made with gold. Pyrite has a brass color that is less shiny and bright compared to the golden-yellow color of gold. Additionally, gold often comes alloyed with silver.

If the alloy contains a higher concentration of silver, then gold will have a white-yellowish color. One of the easiest ways to tell gold apart from pyrite is paying close attention to the shape.

Pyrite minerals often have angular shapes that have sharp edges and corners. Alternatively, pyrite can also resemble a cube, octahedron, or pyritohedron. On the other hand, gold nuggets have a much softer appearance with often round and polished edges. Crystalline pieces of gold can often come in shapes that resemble a pyrite mineral. When in doubt, the best advice is not to rely solely on the shape test.

Gold and pyrite have significantly different specific gravities. When comparing pieces of gold and pyrite of similar sizes, the gold piece should be much heavier. However, gold often comes in alloys.

Some of the metals that gold forms alloys with often have a similar specific gravity to pyrite. In those situations, alloys with low gold content can have a similar specific gravity to pyrite. Still, alloys with significant gold content will always weigh more than pyrite. Striations are fine parallel lines only found on the face of pyrite, lines gold never has.