Here's why:

* Softer than calcite: Galena has a Mohs hardness of 2.5, while calcite has a hardness of 3.

* Metallic luster: Galena has a distinctive metallic luster, often described as lead-grey.

* Cubic cleavage: Galena breaks along perfect cubic planes, forming cube-shaped fragments.

Important Note: While galena fits the description, it's always best to confirm your identification using additional tests and observations, such as streak color (gray for galena) and specific gravity (7.5 for galena).