* Softer than Calcite: Calcite has a Mohs hardness of 3. Pyrite has a hardness of 6-6.5, making it harder than calcite. However, the question states it's softer than calcite. This could be a misinterpretation, or the mineral might be a weathered or altered form of pyrite.
* Metallic Luster: Pyrite is known for its brassy yellow color and metallic luster.
* Cubic Cleavage: Pyrite crystallizes in the cubic system, which results in perfect cubic cleavage.
Other possibilities:
While pyrite is the most likely candidate, there are other minerals that could fit the description:
* Chalcopyrite: This mineral also has a metallic luster and can exhibit cubic cleavage, but it has a brassy yellow color with a greenish tinge.
* Galena: Galena has a metallic luster and perfect cubic cleavage. However, it is typically lead gray in color, not brassy yellow.
To be sure, you'd need to consider additional properties like color, streak, and density.
