Medium: 3.00-4.00 cm
Large: 4.00-5.00 cm
Light blue anhydrite.
The name anhydrite comes from the Greek and means "without water". It refers to the absence of water in the crystallization of the mineral, as opposed to gypsum (hydrated).
It is very common in salt deposits, but it is very rare to find it crystallized.
The piece you receive may differ slightly from the photo shown as the minerals are natural and no piece is identical. The size is approximate.