Why I am starting with Olivine: Olivine is one of the most abundant mineral in the mantle and its properties make my research possible! Plus its very pretty and that’s what my engagement ring is made of! So here we go!
Olivine:
From Wikipedia: magnesium iron silicate with the formula (Mg,Fe)2SiO4. It is one of the most common minerals on Earth, and has also been identified in meteorites, the Moon, Mars, in the dust of comet Wild 2, and within the core of comet Tempel 1.
Mineral data – most of this is what you use to identify the mineral so… the general public doesn’t really care about most of these but I’ll put them here anyways…
Composition Olivine Group: (Mg,Fe)2SiO4
Forsterite (Fo): Mg2SiO4
Fayalite (Fa): Fe2SiO4
Color: Green! Yellow to yellow green and olive green (Hence the name)
Crystal Habit: massive to granular
Crystal system: Orthorhombic
Cleavage: poor ( {001} good, {010} distinct )
Fracture: Conchoidal – brittle
Hardness: 6.5-7
Luster: vitreous (glassy)
Streak: white
Optical properties: biaxial
Composition notes:
– Most olivine exists between Fosterite and Fayalite, and the majority is fosterite rich.
– You can also get Manganese (Mn) substituted in and form tephrolite (Te) Mn2SiO4
Uses: a clear gem variety is called peridot. It is also used as a refractory sand to make molds for certain types of casting procedures in foundries and infrequently as an abrasive. It can also be used in CO2 sequestration
Why is it important:
– The mantle is dominantly olivine and thus the anisotropic nature of the olivine splits seismic waves and allows for studying the mantle flow patters which is my thesis. Cool huh?
– At higher pressures and temperatures olivine is not stable (it also isn’t stable at surface pressures and temperatures)
– At around 400km depth in the mantle olivine undergoes a change from an olivine structure to a spinel structure. This causes an increase in seismic velocity called the 410 discontinuity
– Olivine is more important to me because well I’m a seismologist and I study the deep mantle. Which I think is the most bad ass thing to study! But that’s just me
Chrysolite: A golden yellow variety of peridot. It supposedly can help prevent fever and madness.
Photos:
Gem quality (the pretty ones):
Hand sample:
Thin section:
In rocks:
Discussion:
To me olivine represents something primitive and deep. The mantle is olivine and the oceans crust is basalt which usually has a fair deep of olivine in it. Basaltic volcanoes like Hawaii’s Kailua also come to mind as well as the deep rich green. If you were looking for a mineral to sum up the whole earth well… this would be one of them! In my mind.
Leave a Reply