Framework silicate.
Ring silicate
Crystal system: trigonal (-)
Colour in hand specimen: black
Hardness: 7
Colour in plane polarised light: typically brown-green or green
Pleochroism: strongly pleochroic in many colours
Relief: moderate
Birefringence: typically 2nd order
Ring silicate
Crystal system: trigonal (-)
Colour in hand specimen: black
Hardness: 7
Colour in plane polarised light: typically brown-green or green
Pleochroism: strongly pleochroic in many colours
Relief: moderate
Birefringence: typically 2nd order
Phylum: Arthropoda
Class: Trilobita
Pygidium (tail)
Thorax (body)
Cephalon (head)
Paired appendages (not often preserved)
Three lobed longitudinal division of body (2x pleural, 1x axial)
Calcitic exoskeleton
Segmented body
Glabella
Eyes (holochroal or schizochroal; only present in some groups)
Eye ridges
Occipital ring
Axial rings
Cambrian to Permian (most common Cambrian to Silurian)
Trilobites lived as planktonic, nektonic, epifaunal and infaunal organisms in deep and shallow marine environments. They lived as predators, filter feeders, deposit feeders, particle feeders, scavengers and even symbiotically.
By looking at the functional morphology of the trilobite in question you can be more specific about how it lived, by looking at body shape, size, legs, eyes and other characters.
Trilobites were very abundant during the Palaeozoic. Their preservation potential was increased further as they moulted their exoskeletons periodically as they grew. This means that one trilobite left numerous hard skeletons or partial skeletons as it grew, each of which has the potential to fossilise.
Phylum: Arthropoda
Class: Trilobita
Pygidium (tail)
Thorax (body)
Cephalon (head)
Paired appendages (not often preserved)
Three lobed longitudinal division of body (2x pleural, 1x axial)
Calcitic exoskeleton
Segmented body
Glabella
Eyes (holochroal or schizochroal; only present in some groups)
Eye ridges
Occipital ring
Axial rings
Cambrian to Permian (most common Cambrian to Silurian)
Trilobites lived as planktonic, nektonic, epifaunal and infaunal organisms in deep and shallow marine environments. They lived as predators, filter feeders, deposit feeders, particle feeders, scavengers and even symbiotically.
By looking at the functional morphology of the trilobite in question you can be more specific about how it lived, by looking at body shape, size, legs, eyes and other characters.
Trilobites were very abundant during the Palaeozoic. Their preservation potential was increased further as they moulted their exoskeletons periodically as they grew. This means that one trilobite left numerous hard skeletons or partial skeletons as it grew, each of which has the potential to fossilise.
Orthosilicate
Crystal system: tetragonal (+)
Colour in hand specimen: reddish brown, yellow, grey, green or colourless
Hardness: 7.5
Colour in plane polarised light: colourless to pale brown
Pleochroism: very weak
Relief: high
Birefringence: 0.042-0.065; 3rd order green to 4th order green
Extinction: straight
Twinning: rare
Orthosilicate
Crystal system: tetragonal (+)
Colour in hand specimen: reddish brown, yellow, grey, green or colourless
Hardness: 7.5
Colour in plane polarised light: colourless to pale brown
Pleochroism: very weak
Relief: high
Birefringence: 0.042-0.065; 3rd order green to 4th order green
Extinction: straight
Twinning: rare