Phylum: Brachiopoda
Two valves (brachial and pedicle)
Bilateral symmetry
Growth lines
Adductor and ductor muscle scars
Pedicle
Commissure
Gape
Teeth and socket (articulates; no teeth or socket in inarticulates)
Cambrian to present
Marine
Attach to hard substrates using pedicle
Filter feeding
Sessile
Infaunal, epifaunal, reclining
Apparent decrease in diversity over time
Limited to marginal environments in the modern ocean
Adductor muscle used to close shell, ductor muscle used to open shell
Yale Peabody Museum of Natural History: differences between bivalves and brachiopods
Cortland Paleo, Brachiopoda: brachiopod morphology and ecology information
]]>Phylum: Brachiopoda
Two valves (brachial and pedicle)
Bilateral symmetry
Growth lines
Adductor and ductor muscle scars
Pedicle
Commissure
Gape
Teeth and socket (articulates; no teeth or socket in inarticulates)
Cambrian to present
Marine
Attach to hard substrates using pedicle
Filter feeding
Sessile
Infaunal, epifaunal, reclining
Apparent decrease in diversity over time
Limited to marginal environments in the modern ocean
Adductor muscle used to close shell, ductor muscle used to open shell
Yale Peabody Museum of Natural History: differences between bivalves and brachiopods
Cortland Paleo, Brachiopoda: brachiopod morphology and ecology information
CaCO3
Non-silicate
Crystal system: trigonal (-)
Colour in hand specimen: white
Cleavage: rhombohedral
Hardness: 3
Colour in plane polarised light: colourless
Pleochroism: none
Relief: low
Birefringence:0.172-(0.190); >4th order
Extinction: inclined
Twinning: lamellar, common
M540 Calcite with banded hematite
Egremont, Cumberland
Mass of acicular (needle-like) calcite crystals
Colourless with some grey and red impurities
M541 Calcite
Iceland spar
Iskifjördhr, Iceland
Single crystal of calcite
Colourless, transparent
Hardness 3
Observe the double refraction
Rhombohedral cleavage (three cleavages)
M542 Calcite vein material
Minsterley, Shropshire
Rhombohedral cleavage (three cleavages)
Pearly lustre
Hardness 3
CaCO3
Non-silicate
Crystal system: trigonal (-)
Colour in hand specimen: white
Cleavage: rhombohedral
Hardness: 3
Colour in plane polarised light: colourless
Pleochroism: none
Relief: low
Birefringence:0.172-(0.190); >4th order
Extinction: inclined
Twinning: lamellar, common
M540 Calcite with banded hematite
Egremont, Cumberland
Mass of acicular (needle-like) calcite crystals
Colourless with some grey and red impurities
M541 Calcite
Iceland spar
Iskifjördhr, Iceland
Single crystal of calcite
Colourless, transparent
Hardness 3
Observe the double refraction
Rhombohedral cleavage (three cleavages)
M542 Calcite vein material
Minsterley, Shropshire
Rhombohedral cleavage (three cleavages)
Pearly lustre
Hardness 3
Sheet silicate
Crystal system: monoclinic (+) (-)
Colour in hand specimen: green
Cleavage: one, good
Hardness: 2-3
Colour in plane polarised light: colourless or green
Pleochroism: weak to moderate
Relief: low
Birefringence: anomalous (blue or brown colours that do not appear in the Michel-Levy chart)
Extinction: straight
Sheet silicate
Crystal system: monoclinic (+) (-)
Colour in hand specimen: green
Cleavage: one, good
Hardness: 2-3
Colour in plane polarised light: colourless or green
Pleochroism: weak to moderate
Relief: low
Birefringence: anomalous (blue or brown colours that do not appear in the Michel-Levy chart)
Extinction: straight
Many minerals display very fine, parallel, straight lines called cleavage. Cleavages are the manifestation of planes of weakness within the crystal structure of the mineral. A single crystal may display cleavage in more than one orientation. For example, amphiboles have cleavages which intersect at ~56°, whereas pyroxenes have cleavages which intersect at 90°.
Chain silicate
Crystal system: monoclinic (+)
Colour in hand specimen: black
Cleavage: two at 90°
Hardness: 5.5-6
Colour in plane polarised light: colourless, pale brown or pale grey
Pleochroism: variable weak to moderate
Relief: moderate
Birefringence: 0.018-0.033; 1st order pink to 2nd order orange
Extinction: inclined
Twinning: simple, common
Clinopyroxene contains calcium. It encompasses a range of solid solutions from (Mg,Fe)2[Si2O6] to Ca(Mg,Fe)[Si2O6]. The physical and optical properties detailed above refer to augite, a clinopyroxene common in mafic igneous rocks.
Chain silicate
Crystal system: monoclinic (+)
Colour in hand specimen: black
Cleavage: two at 90°
Hardness: 5.5-6
Colour in plane polarised light: colourless, pale brown or pale grey
Pleochroism: variable weak to moderate
Relief: moderate
Birefringence: 0.018-0.033; 1st order pink to 2nd order orange
Extinction: inclined
Twinning: simple, common
Clinopyroxene contains calcium. It encompasses a range of solid solutions from (Mg,Fe)2[Si2O6] to Ca(Mg,Fe)[Si2O6]. The physical and optical properties detailed above refer to augite, a clinopyroxene common in mafic igneous rocks.
Rocks can be classified according to their colour index (CI). This describes the proportion of ferromagnesian minerals, such as olivine, pyroxenes, amphiboles and biotite mica, they contain. Colour index is measured in volume percent. The terms used to describe the varying proportions of ferromagnesian minerals are:
Phylum: Cnidaria
Class: Anthozoa
Radial or biradial symmetry
External skeleton
Septa
Tabulae
Ordovician to present
Tabulate, rugose: Ordovician to Permian (extinct at P/T extinction)
Scleractinian: Triassic to present
Colonial or solitary
Filter feeding
Reef builders
Remember, although the most well-known modern corals enjoy a symbiotic relationship with photosynthesising algae (Zooxanthellea) many modern corals do not. When thinking about Palaeozoic corals do not assume that they lived as well known corals do now.
Corals built their skeletons out of aragonite (Ordovician to Permian) or calcite (Triassic to recent). They are often preserved as moulds, casts, intact or replaced.
Phylum: Cnidaria
Class: Anthozoa
Radial or biradial symmetry
External skeleton
Septa
Tabulae
Ordovician to present
Tabulate, rugose: Ordovician to Permian (extinct at P/T extinction)
Scleractinian: Triassic to present
Colonial or solitary
Filter feeding
Reef builders
Remember, although the most well-known modern corals enjoy a symbiotic relationship with photosynthesising algae (Zooxanthellea) many modern corals do not. When thinking about Palaeozoic corals do not assume that they lived as well known corals do now.
Corals built their skeletons out of aragonite (Ordovician to Permian) or calcite (Triassic to recent). They are often preserved as moulds, casts, intact or replaced.