Which preposition to use with rectangular

in Occurrences 3%

Everywhere appeared extensive patches, each of a single colour, in every tint between deep red and yellowish green, and so distinctly rectangular in form as irresistibly to suggest the idea of artificial, if not human, arrangement.

at Occurrences 1%

Pinnules ovate or oblong, truncate, nearly rectangular at the base, sharply toothed and covered beneath with chaff and hairs.

with Occurrences 1%

The box was rectangular with an oval center; a thin piece of stone lay in the oval, tawny and flaked.

Which preposition to use with  rectangular