Contact | RSS | EN | DE | EL | ES | FR | IT | RU

Geology glossary

Updated: Feb 1, 2023 22:13 GMT -

obsidian

Volcanology
Obsidian from the Rocce Rosse lava flow on Lipari island (Italy)
Obsidian from the Rocce Rosse lava flow on Lipari island (Italy)
Black volcanic glass
Obsidian is a naturally occurring glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly through the glass transition temperature and freezes without sufficient time for crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid. Because of the lack of cr... Read all

olivine

Minerals
Olivine from basalt lava on Hawai'i (image: By <a rel="nofollow" href="https://www.flickr.com/people/114641806@N08 "target="_blank">incidencematrix</a> - <a rel="nofollow" href="https://www.flickr.com/photos/incidencematrix/23999338641/" target="_blank">Basalt with Olivine</a>, <a href="https://creativecommons.org/licenses/by/2.0" title="Creative Commons Attribution 2.0">CC BY 2.0</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=64113627" target="_blank">Link</a>)
Olivine from basalt lava on Hawai'i (image: By incidencematrix - Basalt with Olivine, CC BY 2.0, Link)
Olivine is one of the earth's most common rock-forming silicate minerals, typically contained in mafic to ultrafafic magmatic rocks with low silica content (e.g. basalt, gabbro, peridotite), which make up much of the earth's upper mantle, the oceanic crust and lava flows etc from basaltic shield volcanoes on land.
Its name refers to its often olive-green color.
Nameolivine
Category
Formula(Mg2+, Fe2+)2SiO4
Crystal systemorthorhombic
ColorYellowish-green to olive green
StreakNone
LusterVitreous
Crystal habitMassive to granular
Mohs hardness6.5–7
Specific weight3.2-4.5
Uses
Other
Chemically, it combines two interchangeable ions of magnesium (Mg2+) or iron (Fe2+) with one silica ion (Si4+) in a densely-packed crystal lattice. The two end-members from this compositional range are forsterite (magnesium-olivine, Mg2SiO4) and and fayalite (iron-olivine, Fe2SiO4). In rare cases, Mg/Fe can also be replaced by calcium (Ca), manganese (Mn), or nickel (Ni). Read all
Try our free app!
Volcanoes & Earthquakes - new app for Android
Android | iOS version

More on VolcanoDiscovery

Sources: VolcanoDiscovery / VolcanoAdventures and other sources as noted.
Use of material: Most text and images on our websites are owned by us. Re-use is generally not permitted without authorization. Contact us for licensing rights.
Volcanoes & Earthquakes
VolcanoDiscovery Home
Volcanoes | Earthquakes | Photos | Volcano News | App
Adventure & Study Travel
Tours to Volcanoes and Volcanic Areas: walking tours, photo tours, study tours
Tours & Dates | FAQ | About us
Get our newsletter!
Company info
Contact | Legal info | Terms & conditions
Follow us
Follow us on facebook Follow us on Instagram Follow us on Twitter Visit our Youtube channel
EN | DE | EL | ES | FR | IT | RU
VolcanoDiscovery GmbH, Germany, Reg. nr.: HRB 103744, EU Tax Id: DE 310 395 322 owned and created by
Dr. Tom Pfeiffer, volcanologist, volcano photographer, tour organizer member of
IAVCEI
Volcanological Society
Ecotourism Greece
Insured by R+V
VolcanoDiscovery © 2004- All Rights Reserved | Privacy - cookie settings