Here's a breakdown:

* Crystal Structure: Minerals are formed from a specific arrangement of atoms in a repeating three-dimensional pattern called a crystal lattice.

* Cubic Lattice: In a cubic crystal system, the atoms are arranged in a cube-like structure. This means that the distances between atoms are equal in all three dimensions, and the angles between the faces of the cube are all 90 degrees.

* External Shape: The external shape of a mineral crystal reflects its internal crystal lattice. A cubic crystal structure will naturally produce a cube-shaped mineral crystal.

Examples of Cubic Minerals:

* Halite (Rock Salt): NaCl

* Galena: PbS

* Pyrite (Fool's Gold): FeS2

Important Note: While a cubic crystal structure *tends* to produce cubic crystals, external factors during mineral formation can influence the final shape. Factors like:

* Growth Conditions: Temperature, pressure, and the presence of impurities can affect crystal growth.

* Twinning: This happens when multiple crystal lattices grow together, sometimes creating unusual shapes.

* Fracturing and Cleavage: Minerals can break along specific planes, even if their original shape was cubic.

So, even though a cubic crystal structure is the primary reason for a cubic mineral shape, other factors can influence the final appearance of the mineral.