Outcrop of bedded gray rock, fingers for scale. Halfway up the outcrop is the base (or is it the top?!?) of a bed with dark internal laminations. Midway across these laminations are folded back on themselves.
Isoclinal soft-sediment slump/drag #FridayFold in graywacke, Bakers Beach, CA. ⚒️
#FridayFold in blueschist, Kayak Beach, Angel Island, San Francisco.
Big red boulder of chert behind a small green boulder. The bedding in the chert is folded into a sideways V shape. No scale.
#FridayFold red chert at Black Sands Beach, Marin Headlands ⚒️
Photo of dark and light rock layers coming across the view at an angle with the layers going in a circle in a distance. The layers are partially submerged in water with the sea in the distance.
The Ladies Skerrs Dome, part of the larger Berwick Monocline, on the shore. It’s composed of sandstones, limestones, and mudstones. #FridayFold ⚒️🧪
A drawer full of ~3" long samples in low flat cardboard boxes. Sitting atop its box, and overlapping several others, is a slab of kinked, foliated rock.
A #FridayFold I found in a drawer full of archived samples at the state geological survey. ⚒️
Flat white slab of gypsum showing layers of grey that has different levels of deformation, some layers very squiggly. There’s an uneven fault through the middle. It sits on a black background. At the Canadian Museum of Nature.
I’m obsessed with this slab of gypsum!! Look at all the squiggly folds and faulting showing the deformation of the evaporite!! #FridayFold #FaultFriday ⚒️🧪
Shiny wet outcrop of foliated rock with subhorizontal dip, brown water in front. A student in a hooded rain jacket gives it two thumbs up.
Big kink folds in phyllite at Totier Creek Reservoir spillway near Scottsville, VA, on yesterday's (rainy) Physical Geology field trip:
#FridayFold
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Specimen on mounted on a green background below a title that says FOLDING. The specimen is brown and is a zig zag with the high hump on the left labeled ANTICLINE and the low bump to its right labeled SYNCLINE. The label below says: ANTICLINAL AND SYNCLINAL FOLDS IN QUARTZITE BOULDER CO., COLORADO At the Field Museum.
Love this old fold exhibit showing this gorgeous example of a anticline and a syncline. The oldest rock layers are on the bottom which helps identify the type of fold. These formed from pressure caused by compression. #FridayFold #GeoscienceBluesky ⚒️🧪
A #FridayFold of kinked, crenulated phyllite that I saw yesterday while poking around at the Virginia state geologic survey. ⚒️
An outcrop of gray green rock, with some orange staining, cross cut by numerous white veins of quartz, but the veins are very short and stubby. The shape of the veins is kind of like an elongated S. A rock hammer provides a sense of scale.
Back-rotated en echelon tension gashes in sandstone within the Catoctin Formation. #FridayFold
folded rock layers in outcrop with copper coin for scale
#FridayFold Folded quartz veins in the mylonitized Neves metagranite. Memories of @egu.eu Summer School 2018!
⚒️ #geology
outcrop with folded rock formations
#FridayFold folded Sinemurian limestones at Punta delle Rocchette, Southern Tuscany, Italy
#geology #tectonics #structuralgeology
An outcrop of intensely folded layered tan and gray rock. Geologist's hand for scale.
My final #FridayFold from December's visit to Mosaic Canyon in Death Valley NP in California. This one is pretty crazy, with at least two hinges. See if you can make any sense of it. ⚒️
A gray and brown rock about 7 inches long showing lots of very tight zigzag patterns. Left hand fingers for scale.
Gorgeous 😍 tight chevron folds in Noonday Dolomite, upper Mosaic Canyon, Death Valley NP, CA.
#FridayFold
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A greyish rock with white squiggly bands of a white mineral across it.
A greyish rock with large blobby bands of a white mineral across it.
Been saving this all week for you. It’s time for #FridayFold and here’s an appealing cobble from the Nashoba Formation. Old arc-complex multiply deformed metamorphic rocks with lots of iron-containing minerals which are giving it the rusty look here as they weather in our temperate climate.
Callan's hand provides a sense of scale to a relatively flat outcrop of white/tan rock. Within the fine-grained and light colored rock are several thinner brown layers. These zig and zag across the outcrop in great swooping exaggerated U shapes. The hinges of these folds are thicker than the limbs, suggesting passive folding instead of buckle folding. The amount of shortening is ... a lot.
On Fridays, we post folded rocks. Check out these tight/isoclinal folds in layering* within the Noonday Dolomite in upper Mosaic Canyon, Death Valley NP, CA.
* Is it bedding? Transposed foliation? ¯\_(ツ)_/¯
#FridayFold
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Outcrop featuring a medium-sized "W" shaped fold train in gray/tan dolostone between black shale layers. Geologist's left hand at lower left of frame, to provide a sense of scale. A bit of desert grass is visible in the distance.
What a week...
Take a moment to return your mind to the sublime, the ancient, the lithological, the ductile.
#FridayFold
This one's from upper Mosaic Canyon in Death Valley, CA
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Callan grinning with the satisfaction of finding a cool new fold outcrop up a desert canyon. Behind him is a black and tan series of layers 1-2 inches thick, all crunched up into tight folds.
First #FridayFold of 2026 - a new one for me, since I was able to hike further up Mosaic Canyon this year than I have on any previous visit. This appears to be a somewhat shaly subsection of the Noonday Dolomite?
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Close up of a brown finely layered sedimentary unit with a few whitish beds surrounded by whitish beds. It is folded in a >>>> shape.
Slightly zoomed out view of the nose of a recumbent fold in brown sedimentary layers.
Very zoomed out view of the hillside that hosts the folded layer near its top.
A recumbent #FridayFold that appears to be soft sediment deformation, in a cliff above the valley of the Amargosa River downstream from China Ranch. I guess these must be Miocene-aged "China Ranch Beds" but I wasn't able to find out more about the geology. If anyone knows, please enlighten me. ⚒️
Folded dark colored metamorphic rocks of the Proterozoic South Delhi Fold Belt. In the upper right, red arrow points to polyphase folding. Two generations of folding seen. Location is Kumbhalgarh fort in Rajasthan.
Folding in Proterozoic South Delhi Fold Belt, Kumbhalgarh Fort, Rajasthan.
Check out the polyphase folding (red arrow).
Pic- Vivek Singh Grewal.
#FridayFold
Large slab of grey schist with white and grey stripes of various thicknesses that are folded making squiggly lines. It sits on a black plinth in front of a yellow placard with a map of the world and a green column. At National Museums Scotland.
A folded schist from Scotland showing that the different layers react to the tectonic forces, some folding easier than others. #FridayFold ⚒️🧪
More folded + cleaved Coombs Limestone in Rockport, Maine, USA for #FridayFold fun. ⚒️
Pic is a light colored boulder of a high grade metamorphic gneiss, intruded by a quartz vein. The vein shows pytgmatic folding and a hint of a pinch and swell boudinage structure. From a stream in the Pindari Valley, Kumaon Himalaya. November 2025.
Ptygmatic folding, along with a slight pinch and swell structure, in a quartz vein intruding Greater Himalaya gneiss.
Pindari Valley, Kumaon Himalaya.
November 2025.
#FridayFold
A wide hillside, sparsely vegetated, with a geologist in the middle to provide a sense of scale. The field of view is about 60' tall and 100' wide. Cropping out are dozens of folds of various interlimb angles and orientations.
A shot of some lovely crumples -- the #FridayFold -- from the flanks of the Cristo Rey laccolith in w.TX / s.NM. Here, Cretaceous aged shale and sandstone of the Mesilla Valley Formation slid off the adjacent bulge of Eocene magma, piling up in chaotic folds as they moved. ⚒️
Varves white gypsum and dark brown calcite laminations where in the center of the field of view is a prominent set of layers that have been folded and overturned to the left. Particularly striking is the THICK triangles of calcite beneath the anticlines, showing I guess a detaching of the behavior of the asymmetrically folded layers relative to run of the mill symmetric folds below. Fingers for scale.
Asymmetric #FridayFold in Castile Formation evaporites, state line outcrop, Permian Basin, TX/NM. ⚒️
#FridayFold (s) in the Mesilla Valley Fm (ss+sh), adjacent to Cristo Rey laccolith, West Texas / S New Mexico. ⚒️
Silurian greywacke folds at St Abb's next to the North Sea.
#FridayFold Silurian greywacke folds at St Abb's Head.
Steeply-dipping strata on both limbs of a tight upright antiform on the LHS of the piccie. Dunno about RHS, is there a synform there or is it faulted? Waves crash below onto stony beach.
It must be #FridayFold ⚒️ time!
Carboniferous Crackington Formation at Hartland Quay, Devon, UK (similar to Millook Haven further south along the coast, but upright here)
Outcrop of rock with geologist's fingertips for scale. The rock is a vertical face in shade, showing several 5-8 cm thick layers of pink calcite and green chlorite that have been folded into an asymmetric S fold (top to the left). The pink/green couplets show a sharp boundary on the bottom of the chlorite layers, but internally the composition changes gradationally.
A #FridayFold from the Castner Marble of the Franklin Mountains of west Texas:
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