Friday Rocks #37: Porphyroclastic Ultramylonite

Feldspar porphyroblasts in the ultramylonite of the Pofadder Shear Zone
Feldspar porphyroclasts in the ultramylonite of the Pofadder Shear Zone

Porphyoclasts are deformed crystals found in a metamorphic rock. In a mylonite weaker minerals deform though crystalplastic processes and form a “toothpaste” texture. Stronger minerals will try to resist the deformation, but may break and stretch along with the weaker minerals. As the weak minerals recrystallize, they will flow around the remnant stronger minerals.

Feldspathic porphyclast in the ultramylonite of the Pofadder Shear Zone
Feldspathic porphyclast in the ultramylonite of the Pofadder Shear Zone

Do you have a cool rock to share? Submit it to FridayRocks[at]Upsection[dot]com

Friday Rocks #36: Conjugate Deformation Bands

Conjugate Deformation Bands
Conjugate Deformation Bands

Deformation bands are mm wide shear offsets that typically occur in  porous rock such as sandstone at shallow depths (Aydin 1978). Offsets on deformation bands are typically small and may be distributed across the entire length of the structure (cm to kms). Brittle deformation via breaking and crushing of grains creates deformation bands which are filled with a gouge or cataclasite. Deformation bands have important implications for reservoir permeability and will typically host a cement.

Fractures that are at angles less than 90 degrees to each other are called Conjugate fractures. The orientation of fractures and offsets may be used to determine the stress state in the rocks during deformation (Anderson 1942, Jaeger and Cook 1969, Olsson et al. 2004). Assuming the above photo is a 2-D example, how do you think Sigma_1 and Sigma_3 are oriented?

Anderson, E.M., 1942. The Dynamics of Faulting and Dyke Formation with Application to Britain, Oliver and Boyd, Edinburgh, London.
Aydin, Atilla. “Small faults formed as deformation bands in sandstone.” Pure and Applied Geophysics 116.4-5 (1978): 913-930.
Jaeger, J.C., Cook, N.G.W., 1969. Fundamentals of Rock Mechanics, 2nd
ed, Chapman and Hall, London
Olsson, William A., John C. Lorenz, and Scott P. Cooper. “A mechanical model for multiply-oriented conjugate deformation bands.” Journal of Structural Geology 26.2 (2004): 325-338.

Friday Rocks #35: Asbestos in Serpentinite and Blueschist

Asbestos in Serpentine and Blueschits
Asbestos in Serpentinite and Blueschist

The rock in this photo as three components. Serpentinite (Green-yellow in photo), blueschist (blue-grey in photo), and asbestos (white-green fibrous vein in photo). Blueschist forms through the metamorphism of basalt at high pressure and low temperature. Serpentinite is a metamorphic rock formed in a low pressure environment through a reaction between ultramafic rock from the Earth’s mantle and water. The reaction is called “serpentiniztion” The asbestos mineral is often associated with serpentinite.

I found this rock when scrambling at the bottom of a cliff on the Big Sur coast of California. There were many small faults which sheared and mixed the different rocks types.

How I Stitch My Panorama Photos

All done!
All done!

Wide Angle lenses make it easy to capture big scenes. Not everyone has a wide lens, so there is a nice work around for capturing those large scenes. It takes a combination of taking multiple photos across the scene and some post-production software to combine the photos together.

NOTE: This method of creating panoramas is not unique or original. There are many methods and software out there for creating panoramas. This is just my process.

Step 1: Take the photographs

This is arguably the most important step because if this gets botched then the whole panorama scene won’t work.

The key here is to overlap the pictures. I typically start at the left side of the scene I want to photograph. Take the photo then pan your field of view slightly right. Roughly 30% overlap with the previous photo seems to work well.

Overlap photos in the scene
Pink boxes show regions of overlap.

Remember, take your time and be sure to overlap the photos. I’ve had a couple times where I was rushing to get the photos and missed the overlap by less than a centimeter and ruined the whole panorama. Take your time and overlap.

Step 2: Load photos

Images are opened in Adobe Photoshop.
Images are opened in Adobe Photoshop.

Once your back home and have your photos on your computer. Open up Adobe Photoshop and open all the photos that you want to stitch. In this example I’m stitching five photos together.

Step 3: Photomerge

Navigate to File> Automate> Photomerge…

File> Automate> Photomerge
File> Automate> Photomerge

This opens the Photomerge dialog. Click the “Add Open Files” button to add the photos you’ve already opened to the photomerge dialog. Alternatively, you may navigate to the folder where the photos are stored and add them.

Next we need to toggle some settings. Select the radio button for “Cylindrical” under “Layout”. Click “Blend Images Together” and “Vignette Removal” if you have vignetting in your photos. You may also want to select “Geometric Distortion Correction“, especially if you are combining many photos (~8 or more) together. Play with these settings to see what produces the best results. When you’re ready to go click “OK” and wait for Photoshop to do all the hard work for you.

Photomerge Settings
Photomerge Settings

Step 4: Clean up

precrop

Now that your photos are combined you may notice that there’s some extra space at the edges of your panorama. That needs to be cropped out.

crop
Crop the panorama.

Use Photoshop’s “Crop” tool to clean up the edges of the panorama. This is also the time to check that the horizon is level. Rotate the crop until the guides are level with the horizon and hit “Enter” on your keyboard to finalize the crop.

Step 5: Apply Image

applyimage

 

Create a new layer (Ctrl+N). Navigate to Image> Apply Image (Shift+Alt+Ctrl+A) and click Okay. This is to create a new layer that has the complete panorama for editing. To finish up adjust the levels, curves, brightness and contrast as you see fit to create a nice panorama.

All done!
All done! Click for a larger view of Lions Bay, BC.

Did I leave out or gloss over a crucial step? Let me know in the comments and I’ll fix it. Have a better / quicker / easier method for creating panoramas? I’d love to hear it!

The photos in this example were taken with my Nikon D7000 and a Tokina 11-16mm lens during a hike up The Lions in British Columbia with my friends Kent and Kalina. Thanks for a great day guys!

 

Friday Rocks #34: Fossiliferous Fireplace

During Texas Clay Fest my girlfriend and I stayed at her boss’ lake house at Canyon Lake. The house hadn’t been updated since the 1970s and was so tacky and awesome. My favorite feature of the home was the fireplace mortared together out of local rocks. It provided a great overview of the fossils and limestones from the area.

image image image image image image

Also would make for awesome indoor boulder…