You don’t need to go on a Jules Verne journey down to the center of the Earth, sometimes the center of the Earth is brought up to us! These rocks are examples of peridotite xenoliths. A xenolith is a fragment of rock that becomes enveloped by magma without being melted or incorporated into it. In these… Continue reading A journey to the center of the Earth | Peridotite xenoliths
Category: petrology
Geo Lingo | The Language of Geologists
Does it ever feel like geologists are speaking a different language? With so many different terms to describe and categorize rocks, learning the lexicon of a geologist can be a bit daunting. To help learn some basic geo lingo, here’s a (far from comprehensive) guide of some of the most important classification and terms geologists… Continue reading Geo Lingo | The Language of Geologists
Rocks of Art
Under the cross-polar light from an optical microscope, this thin section of a rock almost looks like it could be stained glass. The grains of olivine and pyroxene in this peridotite sample display vibrant birefringence interference colors. Not all minerals have such vivid hues under a microscope, though. A mineral’s birefringence depends on its refractive… Continue reading Rocks of Art
Eclogite
Besides its aesthetic beauty and awesome vibrant colors, eclogite is a very rare and important rock. Eclogites are mafic metamorphic rocks that are formed in subduction zone settings. They experience metamorphism at extremely high pressures (1.2 GPa), greater than those typical of the Earth’s crust, as well as medium to high temperatures. They are responsible… Continue reading Eclogite
Rapakivi granite
Wolf River Batholith (WI) - 1.45 Ga Ravakipi is a rather unusual, and distinctive, type of granite with rounded orthoclase (K-spar) crystals. These crystals typically have plagioclase rims, and hornblende and biotite are other common minerals present. Image by author
Minnesota Morton Gneiss
Not only is the Morton Gneiss of Minnesota absolutely gorgeous, it’s also really freaking old. Zircon crystals in the gneiss have been dated to ~3.6 Ga [that’s 3.6 billion years old!] At their age, these rocks are from the Archean Eon, the second eon in Earth’s history (the Hadean is the first), which lasted from… Continue reading Minnesota Morton Gneiss
Larvikite
Larvikite - igneous rock from Norway featuring ternary feldspar
Metamorphic Rocks
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Thin sections
Talc-actinolite schist in thin section Images by author
Pegmatite
Red Ace Pegmatite (WI); Lithium feldspar with pink tourmaline