I think Calcite. Calcite is 3 on the hardness scale and sometimes you can break it into cubes. The difference between Calcite and Quartz is that Calcite is a milky white.
cleavage....
A mineral can have varying numbers of cleavage planes, areas where there exists an inclination to cleave when struck or force is applied.. Most mineral crystals exhibit a preferred cleavage in certain directions, but may have cleavage planes in other directions.
Calcite exhibits cleavage in three directions.
cleavage
Tin, by itself is not a mineral, and has no cleavage.
cleavage....
...directions of cleavage...
A mineral can have varying numbers of cleavage planes, areas where there exists an inclination to cleave when struck or force is applied.. Most mineral crystals exhibit a preferred cleavage in certain directions, but may have cleavage planes in other directions.
Cleavage
Two directions of cleavage, at 90 degrees to each other.
Calcite exhibits cleavage in three directions.
cube
Rock salt.
minerals with cleavage break along smooth, flat surfaces in one or more directions.
Calcite's cleavage is a perfectional, 4 directional rhombohedron shape.
The mineral cobaltite, CoAsS, has a brittle fracture, and exhibits good cleavage in three directions.
cleavage