Which term is the smallest group of atoms with the characteristic chemical composition and the basic crystal structure of a mineral?

Which term is the smallest group of atoms with the characteristic chemical composition and the basic crystal structure of a mineral?

• A. Three-point diamond
• B. Unit cell
• C. Twisted stone
• D. Twinned crystal

Answer: (B)

A unit cell is the smallest block of atoms that, when repeated in three-dimensional space, reproduces the mineral’s crystal lattice and carries its characteristic chemical composition. This tiny building block defines both the arrangement of atoms (the crystal structure) and the formula of the mineral; the entire crystal is formed by stacking copies of this cell in all directions. The other terms don’t describe this fundamental repeating unit: a twinned crystal refers to intergrown domains, and the remaining terms aren’t standard descriptors for the smallest repeating unit in a crystal.

A unit cell is the smallest block of atoms that, when repeated in three-dimensional space, reproduces the mineral’s crystal lattice and carries its characteristic chemical composition. This tiny building block defines both the arrangement of atoms (the crystal structure) and the formula of the mineral; the entire crystal is formed by stacking copies of this cell in all directions. The other terms don’t describe this fundamental repeating unit: a twinned crystal refers to intergrown domains, and the remaining terms aren’t standard descriptors for the smallest repeating unit in a crystal.