Webster's 1913 Dictionary
PERICLASE; PERICLASITE
Per "i *clase, Per `i *cla "site, n. Etym: [Pref. peri- + Gr. (Min. )
Defn: A grayish or dark green mineral, consisting essentially of magnesia (magnesium oxide ), occurring in granular forms or in isometric crystals.
New American Oxford Dictionary
periclase
per i clase |ˈperiˌklās, -ˌklāz ˈpɛrəkleɪs | ▶noun a colorless mineral consisting of magnesium oxide, occurring chiefly in marble and limestone. ORIGIN mid 19th cent.: from modern Latin periclasia, erroneously from Greek peri ‘utterly ’ + klasis ‘breaking ’ (because it cleaves perfectly ).
Oxford Dictionary
periclase
periclase |ˈpɛrɪkleɪz, -s | ▶noun [ mass noun ] a colourless mineral consisting of magnesium oxide, occurring chiefly in marble and limestone. ORIGIN mid 19th cent.: from modern Latin periclasia, erroneously from Greek peri ‘utterly ’ + klasis ‘breaking ’ (because it cleaves perfectly ).
The Wordsmith Dictionary