“Salt & Pepper” Sand (Macro)

“Salt & Pepper” Sand (15mm microscopic)

“Salt & Pepper” Sand (microscopic closeup)

*Not actual salt and pepper.

Multicolored Sand (Macro)

Multicolored Sand (15mm microscopic)

Multicolored Sand (microscopic closeup)

*Although this post has Wednesday’s date on it, I’m actually posting it and the other “sand series” posts late Thursday evening.

Green Sand (Macro)

Green Sand (15mm microscopic)

Green Sand (microscopic closeup)

*Although this post has Tuesday’s date on it, I’m actually posting it and the other “sand series” posts late Thursday evening.

So for this week’s deskcrop series, let’s see how much the experts know about their sand. Four distinctive sands on Monday thru Thursday, and then an evil stumper on Friday. If you’re up to the challenge, comment on what you think the composition of the sand is and where it’s from. We’ll find out who knows their sand…

Black Sand (Macro)

Black Sand (15mm microscopic)

Black Sand (microscopic closeup)

*Although this post has Monday’s date on it, I’m actually posting it and the following four “sand series” posts late Thursday evening.

Today we’ll gaze upon two lovely meander bends on the upper reaches of the Wind River, upstream of Dubois, Wyoming.

Meander Bends, Wind River, Wyoming

As pretty and educational as they are, there are even more river features to be seen in a wider GigaPan view from this vantage point…

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I’m still playing catchup, so short writeups for the next few…

Today’s outcrop is a relatively local one. This escarpment in southwest Rooks County, Kansas is formed where a caprock of Tertiary Ogllala Formation conglomerate (of aquifer fame) unconformably overlies chalk beds of the Cretaceous Niobrara Formation (Smoky Hill Member). Elsewhere in western Kansas this same stratigraphic exposure is exposed with badlands topography developed in the chalk. But not here.

Ogallala Conglomerate Capping Niobrara Fm (Smoky Hill Member) Chalk, SW Rooks County, Kansas

The other interesting geologic feature at this locality was a beautiful set of raindrop impressions in the mudcracked Quaternary layers on the quarry floor.

Raindrops & Mudcracks

I believe I’m going to begin to use more Quaternary landforms for some of my upcoming outcrops…

Today’s deskcrop was formed in the violent climactic (ultra?)plinian caldera-forming eruption of Mt. Mazama some 7700 years ago. It is a large pumice ball, with a diameter of almost a foot. I collected it from the forest floor just east of the boundary of Crater Lake National Park. As lightweight as it is, it’s still amazing to me to imagine the power of an eruption that could toss a fragment of rock this size such a distance from the vent. The entire region is covered by a blanket of ash and pumice fragments from this catastrophic eruption – it’s easy to recognize its buff color in roadcuts and borrow pits.

Mt. Mazama Pumice

[Update: A reader e-mailed me to point out this Caltech website that says, "Radiation is associated with blue and amber colors of calcite. Natural radiation interacts with sheared calcite to produce blue colors. An interesting experiment is to break a colorless calcite crystal into chips upto 3 mm in size. When some of the are chips are exposed to ionizing radiation (such as gamma-rays) they turn amber colored. If some more of the same chips are put into hydrolyic press and squeezed (One can use a KBr pellet press such as are used in chemisty laboratories and pressurize the die to the same pressure used to prepare KBr pellets), they will remain colorless. If they are subsequently exposed to ionizing radiation, they will turn blue." Unfortunately, no reference is cited on the website.]

Blue Calcite from the Valentine Mine, Adirondack Mts., New York

This blue calcite comes from the Valentine Mine, near Harrisville, NY in the Adirondack Mountains. This quarry also happens to be the site of my second cousin’s masters thesis (Hi Martha!). It’s a small world.