pyrophoric
adjective
py·ro·phor·ic ˌpī-rə-ˈfȯr-ik 
-ˈfär-
1
: igniting spontaneously
2
: emitting sparks when scratched or struck especially with steel
Example Sentences
Recent Examples on the Web Intel, Nov. 11, 1986 (Aloha): A pyrophoric gas silane cylinder leaks through a valve and catches fire. 
Mike Rogoway, OregonLive.com, 17 July 2017
Mike Rogoway, OregonLive.com, 17 July 2017 Word History
Etymology
New Latin pyrophorus, from Greek pyrophoros fire-bearing, from pyr- + -phoros carrying — more at -phore
First Known Use
1788, in the meaning defined at sense 1