The Petrology Review

 

How the review works

The aim of the review is to establish material that is of scientific merit and specimens, which are good representatives, possessing public potential for display and community events. These two criteria do not necessarily go hand in hand; as a specimen may have a fantastic scientific research potential, but may not be visually impressive. Therefore the specimens are graded against two separate criteria: Scientific Merit (as a numerical value of stars) and Public Engagement (as a Gold, Silver or Bronze status).

For a more in depth look into the review criteria, click on the “Review Criteria” tab in the tool bar above.

 

 

 The Petrology review

Petrology is sub-divided into three main groups: Igneous, Metamorphic and Sedimentary.

The Sedimentary petrology collection is the largest of the three groups, and consists of 74 trays containing 1,132 specimens. The amount of material created a huge dilemma as to which method would suit the review. It was decided to be conducted as a rapid, systematic, tray by tray investigation, rather than an initial overview of the entire collection; followed by an in depth look at a compiled shortlist.

A summary of reviewed material

Limestones & Dolomites, Chalks, Sandstones, Siltstones, Mudstones, Shales, Conglomerates, Hydrocarbons & Organics*, Extraterrestrial rocks, and Features**.

Sian with a few trays.

 

* “Organics” refers to material of an organic nature, this differs to palaeobotany, and features: Amber, Copalite, Jet, Bitumen, Coal and Elaterite.

** “Features” refers to sedimentary rocks which exhibit unusual structures: wave or ripple preservation, Cone-in-cone and Septarian nodules.

 

Day One.

Dr Sian Davies-Vollum led the review with some wonderful and curious specimens being discovered and highlighted some historically important UK material.

Leedm.B.1998.03.0608

Notably the striking landscape marble or Cotham marble (1 Gold star – Leedm.B.1998.03.0608) from Bristol, a highly calcareous stromatolitic limestone and is prized for it’s “landscape” or hedgerow patterns.

Leedm.B.1993.03.0029

Also, Shale with beef (2 Silver stars – Leedm.B.1993.030029) from Charmouth in Dorset, a very distinct shale with a fibrous calcite structure, noted as a Lower Jurassic marker bed.

Leedm.B.TN2965

 

Plus the figured specimen of Rhaetic bone bed (2 Silver stars – Leedm.B.TN2965) from Aust Cliff in Gloucestershire, which exhibits no fossil material but contains numerous fine tapering lenses.

 

In addition, three wonderful and unusual specimens of Magnesian limestone concretions (1 Silver star – Leedm.B.1980.06.0096.1-3) found near Durham.

Leedm.B.1980.06.0096.1-3

The final tray of limestones.

 

The first day of the review managed to cover limestones, dolomites, chalks, shales and mudstones; featuring some striking banded mudstones (not pictured). A lot of material was reviewed, with limited highlights.

 

 

 

Day Two.

The second day of the review commenced with sandstones, and managed to cover conglomerates, siltstones, features, organics and extraterrestrial rocks. These yielded a far greater number of notable specimens, with some surprising discoveries.

Flexible sandstone

One of the highlights was a number of very strange and amazing Itacolumite or Flexible sandstone specimens from India. Click here to witness the flexibility. Also some uncommon but wonderful specimens of Imatra stones (2 Bronze stars – Leedm.B.TN411) from Scotland, odd little concretions often referred to as “Fairy Stones”.

Leedm.B.TN411

Leedm.B.2011.34

 

The ultimate highlight for Sian was a very unusual and rare specimen of Desiccation cracks     (2 Gold stars – Leedm.B.2011.34), as a discontinuous band of pink mud flakes with an unusual lower surface of rip-up clasts.

Leedm.B.2009.076

Another wonderful specimen is a small and often easily overlooked sample of Fulgurite (1 Gold star -Leedm.B.2009.076). A small tube of fuse quartz formed as the result of a lightning striking.

There was also an interesting Jurassic Laminated sandstone (1 Silver star – Leedm.B.2010.50) from Cayton bay in Yorkshire, featuring vertical burrow structures and carbonaceous root deposits with mica flecks.

Leedm.B.2010.50

 

The collection contains numerous Septarian nodules, these are very common, but two noteworthy specimens are (0 Bronze stars – Leedm.B.TN5412); an interesting complete nodule with crack infill in relief, as a result of weathering. The other is (0 Bronze stars – Leedm.B.2011.33), a split nodule in cross section, illustrating the extensity of cracking throughout the calcite cemented nodule.

Leedm.B.TN5412

Leedm.B.2011.33

 

 

 

 

 

 

 

 

Leedm.B.TN1803

 

Leedm.B.1980.06.0062.1-2

Another highlight was a very unusual specimen of Conglomerate (0 Silver stars – Leedm.B.TN1803), featuring numerous small rounded clasts coated in a green film.

 

Along with another wonderfully named conglomerate; Pudding stone (0 Bronze stars – Leedm.B.1980.06.0062.1-2), consisting of rounded agate clasts in a very fine grained matrix. The specimen has been cut and polished to emphasise its structure.

 

 

The Hydrocarbons and organics revealed some striking specimens of Jet and Bituminous Coal with amazing lustres, plus some stunning samples of resin Copalites with organic inclusions.

Leedm.B.1955.61.0229

A particular highlight is this specimen of Amber (1 Silver star – Leedm.B.1955.61.0229) from the Baltic Coast, with some obscured but strange unidentified inclusions.

Leedm.B.TN5396

 

The collection also contains a number of somewhat peculiar specimens know as Cone-in-cone           (1 Silver star – Leedm.B.TN5396), these are sedimentary features as a series of concentric cones nested inside each other.

 

 

Lastly, the extraterrestrial material comprises of four Pallasite Meteorites from various locations around the world. Two of the specimens are whole and two occur as cut cross-sections, revealing the striking interior of iron with olivine infill voids (3 Gold stars – Leedm.B.1985.05.01) from the Haviland Crater in Kansas, USA.

Leedm.B.1985.05.01

Looking at the larger specimens.

 

The review covered 1,132 specimens, establishing the following summary.

Gold = A truly amazing specimen; Silver = A very good specimen that has great potential; Bronze = A good specimen which can demonstrate a particular feature; Clear = A specimen that has limited visual qualities.

3 stars = High scientific importance; 2 stars = Moderate scientific importance; 1 star = Fair scientific importance; 0 stars = Supported by limited or no documentation.

 

Summary of the Sedimentary petrology collection.

 

Strengths

1) There are good suites of sedimentary rocks collected from the region. This is particularly true for rocks originating from the Carboniferous Coal Measures. They could be used to ‘tell a story’ about the rock sequences in which coal is found and the significance of these in the region.

2) There is a good breadth of sedimentary rock types in the collection with most key rock types included. This range of rocks can be used as a basis for teaching sedimentary petrology and interpretations of sedimentary rocks.

3) There are a number of unusual sedimentary rocks represented by multiple hand specimens e.g. Itacolumite (flexible sandstone from India) and ‘landscape marble’ (Cotham marble, a stromatolitic limestone).

Weaknesses

1) There are many unusual and/or interesting samples that lack information about where they were collected. This lack of information makes it difficult for any researcher to place these samples into stratigraphical or geographical context.

2) Some of the samples are in need of cleaning and preparing to reveal details of their petrology.

3) Apart from a collection made from central Europe, most specimens come from the UK.

 

I would like to say a heartfelt “thank you” to Sian for reviewing this volume of material, and bringing to light such an interesting and often overlooked series of rocks over the two intense, but fun days.

 

The sedimentary petrology, along with all the other collections are open and free for anyone to view by appointment, just call Leeds Discovery Centre on 0113 378 2100 or email discovery.centre@leeds.gov.uk