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20 August 2022

Two erratics from coastal Maine

Happy Saturday! Here are two erratics (glacially transported boulders) that I saw last week in coastal Maine. This one shows prominent subparallel striations: And this one, in the town of Penobscot, next to the greasy spoon called Bagaduce Lunch, shows aligned feldspars that suggest magmatic flow: Nothing like a good erratic to get the weekend started off right!

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18 August 2022

Quarrying soapstone

Earlier this summer, I was lucky enough to visit a soapstone quarrying operation in Schuyler, Virginia, right on the Albemarle/Nelson County line. These soapstone bodies are metamorphosed ultramafic intrusions into the Neoproterozoic sedimentary deposits of the Lynchburg Group. The protolith peridotite sill crystallized at ~580 Ma, meaning the host sediments are older than that (but younger than the Grenvillian basement complex that underlies both). Then both plutonic rock and sedimentary …

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21 February 2017

Q&A, episode 3

A reader asks about the use of zircons in isotopic dating, and the argument for submerged continental crust beneath Mauritius.

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11 January 2017

More Messengers from the Mantle

Since I showed off the 3D kimberlite intrusion breccias yesterday, I feel as if I owe you some other photos from that lovely exhibit at the IGC. I apologize for the poor quality of these photos – the gorgeous samples were behind glass and brightly lit, which made photography difficult. But the rocks are sooooooooo pretty, I think you’ll enjoy viewing them just the same. Let’s start with a gargantuan …

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23 April 2016

Mineral surfaces under the SEM: 6 new micro-GigaPans

As mentioned yesterday, my student Robin has been having some success lately in making GigaPan-scale imagery using the new desktop scanning electron microscope that our division acquired. They aren’t as super-high resolution as most of the other GigaPan images I post here, but they are very, very small – and thus expand the scope of our imaging initiative. Enjoy exploring: find cleavage planes, microscopic plumose structures, examples showing the constancy …

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2 April 2016

Five new GIGAmacro images

Here are a few new images I’ve been working on with my home-based Magnify2 imaging system from GIGAmacro. Strophomenid brachiopods from Mississippian Mauch Chunk Formation, West Virginia: Link Boninite from New Caledonia: Link Lepidodendron scale-tree bark from Poland: Link Potassium feldspar crystal, from a pegmatite: Link Catoctin Formation greenstone from a feeder dike east of Linden, Virginia: Link Enjoy exploring them for details.

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17 March 2016

A GIGAmacro view of the front and back of an anorthosite cobble

Here are two views of a single anorthosite cobble, collected in the Adirondack Mountains of upstate New York: Raw, natural surface: Link Slabbed and polished surface: Link As you zoom in and explore these GIGAmacro images, see if you can find the delicate little “necklaces” (reaction rims) of garnet wrapping around the few isolated pyroxenes!

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28 April 2015

Epidotized tuff, Tucson Mountains, Arizona

I was in Tucson this past weekend for a book project meeting, and my editor and coauthor and I took a hike on Sunday morning in the Tucson Mountains to Wasson Peak. Not far from the summit, we saw an epidotized tuff, where the fiamme and pumice blobs had undergone reactions to produce pods of epidote, giving the rock a look like a sick dalmatian: This is a cool rock …

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13 November 2014

Gypsum casts? You be the judge — UPDATE: Syneresis cracks!

Silurian aged mud cracks feature small lensoidal features: are they casts of ancient gypsum crystals?

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30 October 2014

Geomystery: what are these white lines?

Esteemed readership, I’ve got a mystery for you. What are these white lines, inclined consistently at a high angle to bedding? I picked up this sample below the “Wall of Death,” on the trail from Wapta Lake below Mount Wapta, en route to the Walcott Quarry of the Burgess Shale. The “zebra-striped” rock is of the Eldon Formation of the Cambrian section in Yoho National Park. At first, I thought …

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