–\tSize: 1 um wide and 5 \u2013 20 um long.
\n–\tUse high power magnification in petrographic microscope.
\n–\tIdentification: sweeping extinction. Microgranular: Dark coloured in ppl. Opaque in reflected light. Porcelaneous: dark or amber in ppl. Shiny white in xpl. Hyaline: speckled colours in xpl.
\n–\tPrimary characteristic of foraminifera, molluscs (bivalve).
\n–\tSecondary characteristic of trilobites, ostracodes.
\n<\/p>\n
–\tSize: ~ 10s to ~ 100s um long
\n–\tUse high power magnification in petrographic microscope, but may also be visible under low power.
\n–\tIdentification: rod-like crystals that undergo unit extinction.
\n–\tPrimary characteristic of brachiopods outer layer.
\n–\tSecondary characteristic of molluscs.<\/p>\n
–\tSize: < 100 um width.\n-\tIdentification: rod-like structures with radiating fiber-like crystals. These radiations will make a V-shaped pattern within the rod. When the stage is rotated, the extinction will move across each rod-like structure (move across to one end and move back to the other end).\n-\tPrimary characteristic of molluscs ONLY.\n\n\n\n
–\tSize: ~250 um(?) in width.
\n–\tIdentification: elongated\/rectangular structures with fan-like radiations pointing in the elongation direction.
\n–\tPrimary characteristic of molluscs ONLY.<\/p>\n
–\tFoliated term is used on calcitic shells while nacreous term is used on aragonitic shells.
\n–\tSize: 0.1 \u2013 0.5 um thickness, 4 \u2013 20 um long and 2 \u2013 4 um width
\n–\tFoliated identification: long thin lamination-like structures that are near parallel or parallel to the shell surface or short irregular fiber-like inclined structures.
\n–\tPrimary characteristic of brachiopods.
\n–\tSecondary characteristic of molluscs, bryozoans, worm tubes. <\/p>\n
–\tNacrerous identification: almost similar to foliated but more polygonal and aragonites may be separated by a films of conchiolin
\n–\tPrimary characteristic of molluscs ONLY.<\/p>\n
–\tSize: relatively larger than other microstructures.
\n–\tIdentification: since these fragments are made of a single (usually calcite) crystal, they will undergo unit extinction. Typical calcite twining may observe (~ 60\/120 type crosses) on the surface. In some samples it may look like a calcite crystal. In others you may observe some morphological features such as an outline of an echinoderm.
\n–\tPrimary characteristic of echinoderms.
\n–\tSecondary characteristic of molluscs, fenestrate bryozoans, sponge spicules.<\/p>\n
–\tSize: few mm or 100 um
\n–\tThese are wedges made of 1st and 2nd order lamellae
\n–\tIdentification: ridge-like elongated structures. Not to be confused with complex prismatic because they could look very very similar.
\n–\tPrimary characteristic of molluscs (bivalve) ONLY.<\/p>\n
–\tSize: fibers are very thin, but often found in large quantities (may be observed under low power).
\n–\tIdentification: elongated fiber-like crystals that stacked around coalesced (side-by-side). They may have a bit of circular radiation pattern. Transverse sections will have fan-like growth lines.
\n–\tPrimary characteristic of corals; Tabulata corals (may also be normal to tabulae). Rugose corals. Scleractinia: (trabecular structures in septal walls, crystals radiating out and upwards)<\/p>\n","protected":false},"excerpt":{"rendered":"
Homogeneous Prismatic – Size: 1 um wide and 5 \u2013 20 um long. – Use high power magnification in petrographic microscope. – Identification: sweeping extinction. Microgranular: Dark coloured in ppl. Opaque in reflected light. Porcelaneous: dark or amber in ppl. Shiny white in xpl. Hyaline: speckled colours in xpl. – Primary characteristic of foraminifera, molluscs … Continue reading Skeletal Microstructures-Carbonate Petrology<\/span>