Arsenopyrite Vs. Marcasite

Arsenopyrite is a popular mineral composed of iron arsenic sulfide.^[1] Marcasite is also a popular mineral and its chemical composition is iron sulfide.^[2]

Quick Facts on Differences of Arsenopyrite and Marcasite

For a quick recap of the differences arsenopyrite and marcasite:

• In terms of crystallography, arsenopyrite is monoclinic while marcasite is orthorhombic.
• For chemical formulas, arsenopyrite is FeAsS while marcasite is FeS2.
• Arsenopyrite streaks grayish-black while marcasite streaks black, brown, dark brown or green.
• While both arsenopyrite and marcasite can be commonly white, arsenopyrite is often gray and marcasite is often brown or yellow.
• Arsenopyrite's specific gravity is higher than marcasite - arsenopyrite ranges from 5.9 to 6.2 and marcasite ranges from 4.85 to 4.92.

Quick Facts on Similarities of Arsenopyrite and Marcasite

The similarities of arsenopyrite and marcasite include:

• Arsenopyrite and marcasite both are opaque.
• In terms of luster, arsenopyrite and marcasite both are metallic.
• Arsenopyrite's rarity is similar to marcasite.

Summary of Arsenopyrite

Arsenopyrite is a mineral that belongs to the pyrite group and is composed of iron, arsenic, and sulfur. It is a common mineral found in hydrothermal veins and metamorphic rocks. Arsenopyrite is commonly associated with other minerals such as pyrite, chalcopyrite, sphalerite, and galena. It has a metallic luster and is often found in a bright silvery color.

Summary of Marcasite

Marcasite is a mineral that is commonly found in sedimentary rocks, and it is a type of iron sulfide. It has a metallic luster, and it is often confused with pyrite, which is also an iron sulfide mineral. However, marcasite is less stable than pyrite and can easily oxidize and become discolored. It is also more brittle than pyrite and can easily break into small pieces.

Table Comparison of Arsenopyrite vs Marcasite