Photomicrographs of Other Detrital Grains

 Hematite ooids illuminated with very strong  transmitted light(conoscopic condenser lens  inserted). Note the reddish-yellow color  indicative of hematite which may be partially  altered to goethite-limonite. Oolitic iron  minerals include hematite, chamosite,  limonite, and siderite

 Jurassic Eisenoolith, Germany

 Hematite, here as oolitic coatings on  carbonate skelital fragments. The hematite in  this sample is opaque, but in very thin  sections, with stronger transmitted light, or in  reflected light, one can commonly distinguish  a dark red to brown color characteristic of this  minerals. Hematitic ooids are normally  indicative of oxidizing marine environments,  as well as paleosoils and weathering horizons

 Silurian Clinton Fm., Pennsylvania

 Detrital micas(muscovite). The grains with the  bright blue(second order) birefringence are  muscovite flakes. They are nearly colorless in  ordinary light. The slightly speckled  texture(reminiscent of birch bark) is  characteristic of micas. Muscovite, because  of its greater chemical stability, is more  common than biotite in most sedimentary  rocks

 Cretaceous Monte Antola Fm., Italy

 A large biotite crystal surrounded by  muscovite. Note brown color, excellent  cleavage, and dark spots which are  'pleochroic halos' formed around minute  inclusions of zircon, apatite, or other  uranium-bearing minerals. Biotite crystals are  normally pleochoic, with colors ranging from  colorless to yellow, brown, red-brown, and  green. Biotite weathers readily and if very  abundant in a sediment one can suspect a  volcanic source

 Ordovician(?) garnet schist, Connecticut

 A biotite grain surrounded by quartz. The  biotite shows third order birefringence colors  and the rough(birch bark) texture typical of  micas. Two small pleochroic halos are also  visible. Biotite can be derived in small  amounts from almost all types of igneous and  metamorphic terrains

 Cambrian(?) Hitchcock  Lake Mbr. of  Waterbury Gneiss, Connecticut

 A detrital chlorite grain. Shows anomalous  birefringence colors(some chorite varieties  have 'ultra blue' colors; others have more  normal low birefringence). The coarseness of  this chlorite grain indicates that it probably is  an alteration of biotite. Chlorite can be  distinguished from clinozoisite(which also has  'ultra blue' birefringence) by the higher relief of  the latter mineral. Chlorite is found in most  source rock types

 Permian Abo Sandstone, New Mexico

 A kyanite crystal showing typical high relief,  long and bladed crystal form, two good  cleavages, and light color(often pleochroic).  Kyanite is only found in high-graded  metamorphic source areas and thus is a  valuable provenance indicator. It has moderate  chemical stability but relatively low abrasion  resistance. Many varieties commonly make it  useful for stratigraphic correlation

 Ordovician(?) schist, Connecticut

 Sillimanite. The fibrous crystal form, pale  brown colr, slight pleochroism, and high relief  are characteristic. Sillimanite is found only in  metamorphic rocks(mainly high-grade schists  and contact metamorphics). This mineral has  moderate chemical stability and relatively low  abrasion resistance

 Ordovician-Silurian schist, Massachusetts

 A large andulusite crystal with excellent 110  cleavage surrounded by muscovite.  Andalusite is characterized by high relief,  color ranging from colorless to  pink(occasionally green, or yellow), variable  pleochroism, and excellent cleavage. It is  most common in schists and contact  metamorphic rocks. Low chemical stability in  surface environments explains its scarcity in  older sediments; rather common in younger  units, however

 Paleozoic andalusite schist, New Hampshire

 A staurolite crystal surrounded by  quartz(colorless) and muscovite(stained red in  this section). Staurolite has brownish color,  moderate relief, moderate pleochroism,  abundant inclusions, and prismatic crystal  habit with weakly developed cleavage. It is an  excellent indicator of a schistose  metamorphic source. Detrital grains are rarely  well crystallized

 Ordovician schist, Connecticut