ClipArt ETC
"...a combination of these two tetrahedra, and represents a crystal of blende, in which the four larger faces are dull and striated, whilst the four smaller are bright and smooth." -The Encyclopedia Britannica 1910

Combination of two Tetrahedra

"...a combination of these two tetrahedra, and represents a crystal of blende, in which the four larger…

The illustration "shows how the octahedron with furrowed edge may be constructed from two interpenetrating tetrahedra (shown in dotted lines)." -Britannica, 1910

Octahedron with Furrow Edge

The illustration "shows how the octahedron with furrowed edge may be constructed from two interpenetrating…