sectile

adj.
Of or relating to a mineral that can be cut or severed smoothly by a knife but cannot withstand pulverization.

[Latin sectilis, from sectus, past participle of secāre, to cut.]

sectility sec·til'i·ty (-tĭl'ĭ-tē) n.

Can be cut by a knife, with a shaving curling away, like cerargyrite (“horn silver”) and some of the softer metals.