Body-centered tetragonal carbon (bct-carbon) is a very hard material produced from graphite under high pressure at room temperature. Looking perpendicular to the slices  and , its structure looks hexagonal; from the slice  it appears to be built from small squares. In this Demonstration you can vary several parameters of the 3D atomic structure.
The chemical bonds of the squares of carbon atoms are colored red; the chemical bonds between squares of different layers are colored green.
Try the various viewpoints from the drop-down menu or drag to rotate the crystal.
The "slice" setter bar lets you restrict the atoms displayed to one of three slices of the crystal.
The "show" setter bar lets you make the atoms or links invisible.
Use this slider to change the size of the black carbon atoms.
Use this slider to make the atoms transparent.
Use this slider to change the thickness of the chemical bonds.
Use this slider to make the bonds transparent.
Use this slider to change the size of the carbon squares.
Use this slider to set the distance between the centers of two neighboring carbon squares.
Distance between square layers
Use this slider to change the distance between adjacent layers of carbon squares.
Click this checkbox to reset the crystal parameters to their default value.
Click this checkbox to switch the "floor" display on and off.
Click this checkbox to display coordinate axes.