|an extraordinary or unusual thing, person, or event; an exceptional example or instance.|
|an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.|
|olivine (ˈɒlɪˌviːn, ˌɒlɪˈviːn)|
|1.||Also called: chrysolite an olive-green mineral of the olivine group, found in igneous and metamorphic rocks. The clear-green variety (peridot) is used as a gemstone. Composition: magnesium iron silicate. Formula: (MgFe)2SiO4. Crystal structure: orthorhombic|
|2.||any mineral in the group having the general formula (Mg,Fe,Mn,Ca)2SiO4|
|[C18: from German, named after its colour]|
|olivine (ŏl'ə-vēn') Pronunciation Key
An olive-green to brownish-green orthorhombic mineral. Olivine is a common mineral in the igneous rocks, such as basalt and gabbro, that make up most of the Earth's crust beneath the oceans. Chemical formula: (Mg,Fe)2SiO4. ◇ Olivine in which the mafic component consists entirely of magnesium is called forsterite. Chemical formula: Mg2SiO4. ◇ Olivine in which the mafic component consists entirely of iron is called fayalite. Chemical formula: Fe2SiO4.