Montana, Chert, and the 1960s.

Two years ago, this rock really caught my eye while I was caving in the Madison Group of Montana.
First of all, there’s a nifty calcite or gypsum encrusted pocket, which looks much like a sparkly pothole…

(My assumption is that this formed as water seeped through the limestone into a small hole, and then crystallized on the hole’s walls.)
Then there’s the missing chunk, which gives a nice look at a crazy banded chert nodule.

If that chert nodule embodies John Lennon’s “Magical Mystery Tour” era, this nearby chert nodule is more Jackie Kennedy:

Way to keep it classy, chert.

Two-sided Dike

This is one of my favorite cave features here at Oregon Caves National Monument. It’s a quartz diorite dike encrusted with calcite.

Water (carrying minerals) flows through cracks in the marble bedrock. Quartz diorite is less permeable than marble, and when the water is unable to seep through. Instead, it flows down the surface of the dike, coating one side with calcite formations.
This is my favorite example of this, but there’s a much more prominent one along the tour route, so you should visit sometime!
If you’d like to learn more about the caves, you should read Ranger Gaelyn’s fantastic cave tour part one and part two!

Accretionary Wedge 28: Familial Bookcase-crop

This Accretionary Wedge, hosted at Research at a snail's pace, is focused on desk-crops. Normally, this would be very exciting – I have a healthy assortment of rocks. But, unfortunately, I put all my rocks in my storage unit when I moved to Idaho for the summer.

I only remembered about this Accretionary Wedge once I arrived in Oregon with four boxes, none of them containing rocks. Luckily, before I went to Phoenix last week, I was helping clean a bookshelf at my parent’s house in Washington, and happened to take some pictures of my mother’s minerals.

My mother (a painter of caves – seriously!) has a soft spot for colorful minerals and rocks. These are actually examples from her stash of minerals inherited from my grandfather, who was into rock-hounding. My mum has some great childhood stories from these trips, including “Terrifying Mine Experiences Involving Cupcakes,” and “Innocent Encounters with Canadian Mounties.”

I haven’t studied mineralogy much yet, so I’m mainly going to reference that bastion of scientific accuracy: wikipedia.

This Death Tribble is a piece of dogtooth spar, or dogtooth calcite. This usually consists of acute scalenohedrons: twelve triangular faces roughly making up scalene triangles.  They need standing water to allow them to grow, and so are frequently found in limestone caves. (My grandfather, I’m sure, found this in a rock shop – he wasn’t a caver, much less a cave-vandal.)

The only spooky thing about orpiment is that it’s a highly toxic cocktail of arsenic and sulfide, originating through the rapid solidification of hot gases at fumaroles, hot springs, and hydrothermal veins. It can also occur as the decay byproduct of realgar, a mineral of a similar composition that is frequently also found in conjunction with orpiment. (I’m wondering if realgar is in this sample, based on its appearance in google images.) Orpiment has historically been used for poision, medicine, and paint pigment; its present uses include semiconductors, firework pigments, and as an ingredient in Indian depilatories. (Perhaps: “Extreme Hair Remover: Now with Arsenic!” ?)