Structural elements of slate

There are many structural features in a quarry, which influence the properties of a slate and therefore the way of slate mining. This page gives a short overview of structural features which can be seen in a quarry.
The following table gives an overview of the features and their influence.

Pictures

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  Fig. 1: Fold of a thick quartzite bed within two slate quarries (Spain)

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  Fig. 2: Fold of a thick quartzite bed (Detail)

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  Fig. 3: Spatial relation between bedding and fracture cleavage: The angle between S₀-S₁ is highest within the hinge zone of the fold and decreases towards the fold limbs.

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  Fig. 4: Kink-bands occur frequently in slate quarries. This folding style is due to the geomechanically anisotropic character of slates. In Germany slates with obvious kink-bands are not suitable for slate roofing except for rectangular roofing.

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  Fig. 5: En-echelons arrays makes this part unsuitable for slate mining because is blocks will break apart.

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  Fig. 6: An orthogonal joint system facilitates mining of large slate blocks
  [black = cleavage plane]

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  Fig. 7: Gradded bedding with smooth harmonic folds.
  The fracture cleavage runs from upper right to lower left.
  

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  Fig. 8: Ptygmatic folds

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  Fig. 9: Kink folds

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  Fig. 10: Plumose structure. It shows the crackt propagation in joints. Here it shows the crack propagation from the left to the right, caused by the splitting with hammer and chisel during processing. In the field, one can use it as a kind of a field test as a sign or a "true slate".