Most of the Precambrian quartzites in Wisconsin show brecciation with angular quartzite surrounded by white vein quartz, often with cavities and quartz crystals. The blocks shown here are typical of the breccia zone in the Upper Narrows.

Structure/Foliation/ 85_409. Note the relatively quartz rich microlithons (lighter layers) crossing several of the dark layers.

Structure/Foliation/ 85_410. This outcrop is crowded with microlithons of relatively quartz rich material alternating with darker bands from which the quartz is removed.

Structure/Fold/Folds1/85_428.JPG. Kink Folds in Carboniferous Culm facies. England , Hartland Quay, Devon, Eng. [SS225250; 50.995643,-4.531395]

These chevrons are a puzzle. One idea is that they develop from conjugate kinks with the migration of kink boundaries until the final boundary is vertical.

Structure/Fold/Folds1/85_421.JPG. Kink Fold with saddle reef and thrust. Hartland Quay, Devon.

Structure/Foliation/85_518.JPG. Pressure solution and related tension gashes running horizontally across the slide near the large vein. Hartland Quay, Devon, England.

./Structure/Veins/85_425. Encephalon tension gashes in a shear zone. Hartland Quay, Devon, England. The cracks indicate a shear of the top to the right. The orientation of the veins is perpendicular to the long axis of the strain ellipse.

/Structure/Veins/85_439. Folded tension gashes. Welcome, north of Bude, Devon, England

Structure/Fold/Folds1/85_429.JPG. Box fold. Northcott Mouth, N. of Bude, Cornwall, Eng.

./Structure/Veins/85_513. En echelon tension gashes defining a series of parallel shear zones. Millook Haven, Cornwall.

./Structure/Veins/85_514. Tension gashes in a progressive shear. Millook Haven, Cornwall.

/Structure/Veins/85_515. Tension gashes rotated during a progressive shear. Millook Haven, Cornwall.

./Structure/Veins/85_516. Tension gashes in conjugate shears. Millook Haven, Cornwall.

/Structure/Veins/85_517. Tension gashes rotated during a progressive shear. Millook Haven, Cornwall

Typical breccia. Note moderate to steep dip of breccia, multi-phase mineralisation, sharp contact with footwall and subparallel to weakly stockworked veining in hanging wall.

Stockwork vein zone and narrow breccias have not been considered economic in the past. The economic potential of these zones should be re-assessed to reflect present metal prices

Breccia composed of banded quartz-sulphide-chlorite fragments supported in a quartz-sulphide cement.

Banded quartz-sphalerite-chlorite vein with disseminated pyrite. Note coarse-grained quartz and andesite fragments.

Monomict breccia supported by coarse-grained, cockade quartz-galena-sphalerite, crosscut by banded and massive quartz and quartz-carbonate veins. Breccia is offset by late normal faults

These veins of “milky quartz” are often arranged in lovely en echelon series, like these tension

Fluorite mineralisation is continuous over a strike length of 4-km and the characteristic banding of the two lodes persists. Gangue mineralisation-supported inclusions of country rock are common in this interval. Outside of the competent rhyolitic sequence, the lodes rapidly decrease in thickness. Void space never formed or was collapsed before mineral precipitation. In these units, dilational strain was not localized.

Where the two subparallel lodes coincide, mineralisation may reach a fault-normal thickness of 18 meters. Up to 70% of this width can be occupied by massive fluorite. The two lodes have individual thicknesses ranging between 1.5 and 7 meters. The host rocks of the mineralization experienced very low grade Hercynian metamorphism and suffered a further retrograde overprint when the mineralisation formed. This retrograde alteration consists of an assemblage of chlorite + sericite + minor finely disseminated pyrite.

Marble Flooring tiles, Marble Wall cladding tiles

Note the asymmetric bondinage of the quartz vein that continues to the left of the tip of the mechanical pencil.

This another photo from the same several hundred meter thick mylonite zone as above. The cross section view is basically parallel to the lineation and transport direction. Here the asymmetric geometry and

A Flamboyan Shape of Quartz found in Bogor, Indonesia

gashes of the quartzite veins. I have annotated the shear direction in the pictures below. These tension gashes form at right angles (perpendicular) the direction of maximum stretching

we found S and C fabrics as annotated in the picture above, which indicate as sinistral sense of shear. Although not visible in this picture, lineations were present in this outcrop and I found two different sets of foliation.

Bedding-perpendicular vein characteristics (Van Noten et al., submitted). A) Vein refraction of two different vein generations at the competent-incompetent interface. B) A composite vein which comprises several quartz laminae intercalated by thin host rock inclusion bands. C) Lensoid quartz veins, subperpendicular to bedding. D) Veins cross-cutting. E) En-echelon vein and model of vein formation based on the vein geometry.

Bedding-parallel veins (BPV) characteristics (Van Noten et al., submitted). A) BPV cross-cutting a bedding-(sub)perpendicular (BppV) vein. B) Composite BPV interbedded in a pelitic sequence. C) Composite BPV with varying slickenline orientations (shown by black lines) on different quartz laminae. D-F) BPVs vary in thickness along their length and sometimes show a high affinity with the underlying pelites (D&F) but are mostly detached from the upperlying sandstone (E). Furthermore cleavage refracts through the BPV. G) Composite BPVs truncate and offset bedding-(sub)perpendicular veins (BppV).

This conglomerate has been sheared into a lovely L-S tectonite, with X>Y~Z. In other words, it’s mostly lineated, with only a weakly-defined foliation, indicating the stress field was mostly constrictional. (I collected a muddy sample of this stretched-pebble meta-conglomerate, and when I washed it off in the hotel shower the next morning, I was delighted what a cool sample I had selected. It has some awesome structural features; I’ll show it to you some other time…)

This is a sweet example of how you can get different structures developing in different orientations relative to the principal stress directions. In this particular part of the Barberton Greenstone Belt, compression (orange arrows) operated from the top of the photo towards the bottom, and the rock stretched out from left to right (green arrows). Folds formed where granite dikes were compressed, but the same rock in a different orientation was boudinaged… Cool, eh?