1A Collections

TF0311 Ceratite

Thu, 20 Jun 2019 09:48:59 +0100

Title

TF0311

Ceratite

Description

Species

Ceratites

Stratigraphic Range

Triassic

Taxonomy

Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ceratitida

Distinctive Features

Planispiral
Aperture
Body chamber
Ceratitic suture lines
Evolute

Preservation

Internal mould

Advanced notes

Set 1 specimen is a plaster cast

TF0323 Ammonite

Thu, 20 Jun 2019 09:37:02 +0100

Title

TF0323

Ammonite

Description

Species

Parkinsonia parkinsonia

Stratigraphic Range

Jurassic

Taxonomy

Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida

Distinctive Features

Planispiral
Evolute
Ribs
Ammonitic suture lines

Preservation

Calcite has replaced aragonite in the skeleton

Advanced notes

Beware! The specimen in set 2 has a dark circular hole, which you may be tempted to identify as a siphuncle. However remember that in ammonoids the siphuncle runs around the outer edge of the chambers, so this hole is in the wrong place. It is probably there due to eccentricities of the mineralisation process.

Why is it a dark colour when the rest of the shell is white? Generations of Earth Scientists have made the same mistake, their pencil marks fooling others into making the same error.

TF0324 Ammonite

Thu, 20 Jun 2019 09:35:04 +0100

Title

TF0324

Ammonite

Description

Species

Amoeboceras alternans

Stratigraphic Range

Jurassic

Taxonomy

Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida

Distinctive Features

Planispiral
Ammonitic suture lines visible on some moulds
Ribs

Preservation

Most external moulds, few examples of internal moulds, pyritised

TF0325 Ammonite

Thu, 20 Jun 2019 09:14:41 +0100

Title

TF0325

Ammonite

Description

Species

Deshayesites

Stratigraphic Range

Cretaceous

Taxonomy

Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida

Distinctive Features

Planispiral
Ammonitic suture pattern
Evolute
Ribs
Aperture

Preservation

Internal mould, with aperture partially crushed

TF0326 Ammonite

Thu, 20 Jun 2019 09:08:04 +0100

Title

TF0326

Ammonite

Description

Species

Anahoplites splendens

Stratigraphic Range

Cretaceous

Taxonomy

Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida

Distinctive Features

Planispiral
Involute
Ammonitic suture pattern
Ribs

Preservation

Internal mould, pyritised

Advanced notes

For the specimen in set 1 only part of the whole shell is present. The rest has either broken off or not been preserved at all.

TF0327 Heteromorphic ammonite

Mon, 17 Jun 2019 16:42:18 +0100

Title

TF0327

Heteromorphic ammonite

Description

Species

Scaphites

Stratigraphic Range

Cretaceous

Taxonomy

Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida

Distinctive Features

'g' shaped coiled shell
Ribs
Involute
Ammonitic suture lines

Preservation

Internal mould

Advanced notes

Heteromorphic ammonites (such as Scaphites) diversified during the late Cretaceous. They may have lived as planktonic or benthic organisms depending on where the centre of gravity lies in the shell, which is much dependent on the soft parts. Sadly these soft parts rarely preserve.

L521 Quartzite

Mon, 17 Jun 2019 12:42:07 +0100

Title

L521

Quartzite

Subject

Age

Precambrian

Location

Braemar, Aberdeenshire

Description

Hand Specimen

Buff coloured rock.
Almost pure quartz, which has been very well recrystallised.
Faint banding could be original bedding.

Thin-section

Fine to medium grained recrystallised quartz with sutured contacts.

Rock History

The sutured (ragged) grain boundaries and undulose extinction of the quartz grains indicate that this rock formed under relatively low temperature metamorphism. Had the rock been raised to higher temperatures perfect 120° grain boundaries would have formed, and the quartz would not be strained.

Inserting the sensitive tint plate results in the vast majority of grains changing colour in the same way – most of the grains simultaneously display higher interference colours in one orientation, and lower interference colours in the other orientation. This strong fabric was produced by recrystallisation under directed stress, which caused all the grains to elongate in one direction.

Rock Name

quartzite

L520 Quartzite

Mon, 17 Jun 2019 12:38:44 +0100

Title

L520

Quartzite

Subject

Specimen Age

Carboniferous

Location

Coal measures
Corrie, Arran

Description

Hand Specimen

Almost entirely made up of fine sand sized quartz grains. Does not fizz with acid, so no carbonate present. Clean white rock, apart from pink-brown weathering. Dark carbonaceous marks are plant roots.

Thin-section

Subangular quartz grains, typically 0.25 mm across with sutured contacts.

Rock History

The sutured contacts between the quartz grains indicate that this rock has been metamorphosed to a quartzite. This is a very well recrystallised rock. The protolith was a fine-grained quartz arenite (<15% matrix), but we cannot tell how angular or spherical the original grains were as they have been partially dissolved by pressure solution to form sutured contacts.

Rock Name

quartzite