In crystallography, having the form of two pyramids joined base to base, as quartz crystals.

adjective. Consisting of two pyramids placed base to base; having a pyramid at each of the extremities of a prism, as in quartz crystals.

adjective. Having the shape of a bipyramid

"Like a routine play nine hundred and ninety eight spindly human figures stepped forth onto the walls and filed towards the black emptiness arranged around the Core in what a chemist or mathematician might call tetrahedral bipyramidal form."

bistatic  black hole  cell-adhesion  cellsurface  costimulatory