pyrophoric

[ pahy-ruh-fawr-ik, -for- ]

/ ˌpaɪ rəˈfɔr ɪk, -ˈfɒr- /

capable of igniting spontaneously in air.

Origin of pyrophoric

1780–90; < Greek pyrophór(os) fire-bearing (see pyro-, -phorous) + -ic

These two combustibles are in such a state of division, that the residuum is pyrophoric.

A Dictionary of Arts, Manufactures and Mines |Andrew Ure
The residuum of the distillation is pyrophoric and frequently inflames spontaneously, on exposure to the air.

Cooley's Cyclopdia of Practical Receipts and Collateral Information in the Arts, Manufactures, Professions, and Trades..., Sixth Edition, Volume I |Arnold Cooley

pyrophoric

/ (ˌpaɪrəʊˈfɒrɪk) /

(of a chemical) igniting spontaneously on contact with air

(of an alloy) producing sparks when struck or scraped lighter flints are made of pyrophoric alloy

C19: from New Latin pyrophorus, from Greek purophoros fire-bearing, from pur fire + pherein to bear