Crystal Lab

1. Count the atoms: a corner atom is shared by 8 cells (⅛ each), an edge atom by 4, a face atom by 2, an interior atom belongs wholly to the cell.
2. Find Z: the number of formula units in the cell. The viewer counts the atoms for you and divides.
3. Coordination number: click any atom — its nearest neighbours light up and the polyhedron they form is drawn.
4. Holes: in close-packed arrays every atom brings one octahedral and two tetrahedral holes; switch them on in fcc, hcp and simple cubic to see where ions go.
5. Density: ρ = Z·M / (N_A·V). The Calculator tab does it for the cell shown, or for numbers you type.

Each structure has its own page with the cell, coordination and notes. Need a structure type that is not here? Browse the 2,126 prototype structures, each with its atoms on their Wyckoff sites and the symmetry elements of its group.