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Tag: original
Muscovite pegmatite
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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
Ammonite
The Jurassic (early Mesozoic) is known as the ‘Age of the Ammonites,’ as they were the original index fossils used by William Smith. Along with dinosaurs, corals, brachiopods, and molluscs, they were among the hardest hit species during the K-T extinction 65 Ma. Image by author
Native copper
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Prograding Delta Deposits
Typically when you think of a sediment deposit, you think of a fining upwards sequence. That means that the heaviest/coarsest stuff is going to be at the bottom and the lighter stuff is going to be at the top, ‘cause you know, gravity settling. In laterally migrating streams, we see these fining upwards deposits of sand under… Continue reading Prograding Delta Deposits
Obsidian
Volcanic glass - rapid cooling causes minimum crystal growth, which creates a glassy texture
Staurolite
Scoria
Scoria is an extrusive igneous rock formed during volcanic eruptions. It is highly vesicular, meaning that it has many cavities (vesicles) both inside and at its surface. It has a very low density, so for a rock, it’s pretty darn light! Image by author
Larvikite
Larvikite - igneous rock from Norway featuring ternary feldspar
Emily Zawacki, Ph.D. 