Their metallic appearance arises from their being composed of a mineral called Hypersthene.
"A Yacht Voyage Round England"
W.H.G. Kingston
These feldsparites sometimes form mountain masses almost without any admixture of other minerals; but at other times they include augite, which passes into Hypersthene.
"The Student's Elements of Geology"
Sir Charles Lyell
W 1.10 3.23. Hypersthene.
"The Student's Elements of Geology"
Sir Charles Lyell