<![CDATA[1A Collections]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?sort_field=Dublin+Core%2CTitle&page=19&output=rss2 Tue, 09 Apr 2024 21:24:43 +0100 p1acollections@esc.cam.ac.uk (1A Collections) Zend_Feed http://blogs.law.harvard.edu/tech/rss <![CDATA[Graptolite]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/114

Title

Graptolite

Description

Taxonomy

Phylum: Hemichordata

Class: Graptolithina

Diagnostic features

Stick-shape (often branched)

One or both edges may appear serrated

Thecae

Rhabdosome

Stipes

Stratigraphic range

Cambrian to Carboniferous (Dendroids)

Ordovician to Middle Devonian (Graptoloids)

Way of life

Colonial

Planktonic (mostly, although some dendroids were sessile benthonic)

Suspension feeders

Typical preservation

Flattened along bedding planes, normally in shales

Carbonization or pyritization of the animal

Learn about types of preservation

Advanced notes

Graptolites, because of their abundance and variation in morphology are very good index fossils. At a very basic level the angle between the stipes and number of stipes can be used to give a rough age for the fossil, with Early Ordovician graptolites having two stipes with the 'sawtooth' facing each other (pendent), later Ordovician graptolites having a more open oblique or reflex angle between the 'sawtooth' faces, and Siluran graptolites having the 'sawtooth' faces back to back (scandent) or having lost one stipe altogether (for example monograptids).

Specimens

Browse graptolites

graptolite_sketch.png
graptolite_range.png
]]> Thu, 20 Jun 2019 13:10:22 +0100 <![CDATA[Groundmass]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/205

Title

Groundmass

Subject

Rapidly cooled magmas are largely made-up of many tiny crystals. These make up the groundmass.
]]> Fri, 21 Jun 2019 16:06:53 +0100 <![CDATA[Gypsum]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/62

Title

Gypsum

Description

Formula

CaSO4∙2H20

Structure

Non-silicate

Crystal System

Crystal system: monoclinic (+)

Physical Properties

Colour in hand specimen: usually white or colourless
Cleavage: rhombohedral, one perfect, two distinct
Hardness: 2

Mineral Specimens

M530 Gypsum 
Shotover, Oxford 
Single euhedral crystal 
Colourless, transparent 
Hardness 2; Soft – scratched with your fingernail

M531 Massive gypsum 
Nottingham 
Fibrous habit – many fine crystals 
White-cream colour 
Translucent 
Pearly lustre

Mineral Name

gypsum
gypsum_1.jpg
gypsum_2.jpg
gypsum_CS.jpg
]]> Mon, 17 Jun 2019 16:06:30 +0100 <![CDATA[Habit (or form)]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/206

Title

Habit (or form)

Subject

The three dimensional shape of a crystal. The crystal structure of a mineral influences the characteristic habit(s) which it displays. For example, biotite mica tends to display a platy or tabular habit because its crystal lattice is made up of sheets.
]]> Fri, 21 Jun 2019 16:07:39 +0100 <![CDATA[Halite]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/68

Title

Halite

Subject

This mineral is commonly known as rock salt.

Description

Formula

NaCl

Structure

Non-silicate

Crystal System

Crystal system: cubic

Physical Properties

Colour in hand specimen: colourless or white when pure, more typically orange or red due to inclusions of iron compounds, and may also be grey, yellow or blue 
Cleavage: perfect cubic, three planes intersect at 90° 
Hardness: 2.5

Mineral Name

halite
halite_CS.jpg
]]> Mon, 17 Jun 2019 16:31:12 +0100 <![CDATA[Hardness]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/207

Title

Hardness

Subject

Hardness is measured on the Mohs scale. A hard mineral is rigid, resistant to pressure and is not easily scratched. Determining the hardness (or relative hardness) of a mineral in hand specimen can aid your identification of the mineral.
]]> Fri, 21 Jun 2019 16:08:47 +0100 <![CDATA[Hematite]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/58

Title

Hematite

Description

Formula

Fe2O3

Structure

Non-silicate

Crystal System

Crystal system: trigonal (-)

Physical Properties

Colour in hand specimen: black, steel-grey and bright to dull red 
Streak: cherry-red 
Cleavage: none 
Hardness: 5-6

Optical Properties

Colour in plane polarised light: opaque; blood-red in very thin splinter 
Pleochroism: none 
Relief: high

Mineral Specimens

M500 Hematite 
Cumberland 
A concretionary mass showing concentric and radial structure 
Silvery black with a red streak 
Oxidised to dark brown-red in places 
Metallic lustre

Rock Specimens

L310 Breccia 
L311 Conglomerate 
L324 Sandstone, feldspathic arenite 
L326 Sandstone, ferruginous arenite 
L340 Mudstone 
L354 Limestone, shelly
L500 Slate

Mineral Name

hematite
iron oxide
opaques
hematite_1.jpg
hematite_CS.jpg
]]> Mon, 17 Jun 2019 15:53:57 +0100 <![CDATA[Hypabyssal]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/208

Title

Hypabyssal

Subject

Hypabyssal rocks and textures are those associated with very shallow magmatic intrusions, where cooling is moderately rapid. This term is restricted to relatively small intrusive bodies centimetres to tens of metres in diameter.
]]> Fri, 21 Jun 2019 16:09:13 +0100 <![CDATA[Hypermelanic]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/209

Title

Hypermelanic

Subject

Hypermelanic rocks have a very high colour index. That is to say that >90 vol% of the rock is made up of ferromagnesian minerals.
]]> Fri, 21 Jun 2019 16:10:50 +0100 <![CDATA[Inclusion]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/210

Title

Inclusion

Subject

As a crystal grows in a magma, tiny blobs of melt can become trapped in its structure. These are melt inclusions. Small crystals of other minerals can also become trapped. These are mineral inclusions.

Description

Have a look at the alkali basalt (L100), the porphyritic rhyolite (L110) and the garnet schist (L504) in the 1A Reference Series.
]]> Fri, 21 Jun 2019 16:13:23 +0100