Glossary (L – S)

This page provides a glossary of geological terms to be found on the TVRIGS website and elsewhere. It is an evolving document and will grow as the site expands.


L

Liquor Channel (or Conduit)
Wood or stone-lined channel along which alum liquor was transferred between the quarry and the alum-house.


M

Malm
(Obsolete) Chalky-clayey soil or rock, in part equivalent to marl and other impure calcareous rocks. It is also an old name for the Upper Jurassic.
Mineral
Naturally occurring solid element or compound, exclusive of biologically formed carbon components. Has definite composition or range of composition and orderly internal atomic arrangement (crystalline structure), which gives unique physical and chemical properties, including tendency to assume certain geometrical forms known as crystals.

[Source: Leet, L. Don. 1982. Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall]

Mothers
Concentrated liquid residue recovered from casks after roaching alum.
Mudstone
Fine-grained, argillaceous rock generally (though not exclusively) formed in deep quiet water. Mudstone differs from shale in having little or no bedding planes and a ‘blocky’ fracture.


P

Particle Size
When dealing with sediments and sedimetary rocks precise dimensions are applied to the terms clay, sand, silt, etc. The most widely-accepted, and used as an international standard, is the Wentworth-Udden Scale shown below. The list shows particle size limits which, in some instances, may be further subdivided into fine, medium and coarse grades.

Particle Size Table
Size Range Particle
> 256mm Boulder
64-256mm Cobble
4-64mm Pebble
2-4mm Gravel
1/16-2mm Sand
1/256-1/16mm Silt
< 1/256mm Clay

Permian
Named (by Murchison, 1841) after the Perm region of Russia where these beds are well-exposed. The Permian covers an episode in Earth’s history between c.299 million and 251 million years before present. The Permian is further subdivided into Lower, Middle and Upper episodes. Locally, these rocks comprise dolomitic limestones and chemical sedimentary rocks (evaporites), which include halite, sylvinite and anhydrite,deposited during shrinkage of the ancient Zechstein Sea .


Q

Quaternary
Named (by Arduino, 1759) this is the most recent episode in Earth’s history which commenced c.2.5 million years ago and continues into the present day. The Quaternary is characterised by the advance and retreat of continental ice-sheets from high latitudes.
It is divided into the Pliestocene and Holocene epochs. The Pliestocene covers numerous advances and retreats of ice-sheets up to the last retreat (c.20,000 years before present locally), the Holocene covers the time since the last retreat of ice-sheets to high latitudes.


R

Rudaceous Rocks
The coarsest group of detrital sedimentary rocks composed of clasts greater than 2mm across, including pebbles, cobbles and boulders. Rudaceous rocks, from the Latin Rudus meaning ‘rubble’, may form through the lithifaction of talus, fault breccia, alluvial deposits and relict boulder clays known as tillites. When interbedded with marine deposits such beds may be indicative of an unconformity or episode of no-deposition. Another name for water-lain deposits of this grade is conglomerate.


S

Sabkha
The Arabic term sabkha normally refers to broad coastal flats in arid regions known as salt flats, the ‘type area’ is on the Trucial Coast in Abu Dhabi. These environments can be broadly divided into two types;

  • Coastal Sabkha: Comprising a mixture of offshore and wind-borne land-sourced material.
  • Continental Sabkha: Comprising dune-bedded sands and wind-borne carbonate dust from the coast.

Sabkhas are only occasionally flooded and hence evaporation of the flood water leaves behind evaporite deposits (gypsum, anhydrite, halite, etc.)

Shale
Clay-based, argillaceous, sedimentary rock the definition of which varies. Shale tends to be a very fine-grained, laminated and fissile rock. For example the Jet Rock member of the Whitby Mudstone Formation. Rocks having a similar grain-size, but little or no bedding and a blocky fracture, may be referred to as mudstone.
Within the Cleveland ore-field, miners would refer to the argillaceous beds between ironstone seams as shale regardless of grain-size, up to fine sand.
Steeping
The soaking of calcined alum shale in water-filled pits. A process which dissolves the salts released during calcination to produce alum liquor. This stage in processing occurred within the quarry.


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