The points are made of quartzite, a common stone found in the area, chert, a tough, fine-grained rock not from this area, and petrified wood, found in northern Texas and areas of Colorado.
22.
Photos of deep beds of sedimentary rock on Mars suggest that the Red Planet was once a planet of lakes, with water seeping into craters and helping to form layer upon layer of fine-grained rock.
23.
In the Sao Jose do Campestre Massif in Brazil, the syenogranite is a coarse-grained rock composed of microcline, quartz, hornblende, and rare clinopyroxene, together with allanite, as essential minerals ( Benjamin et al ., 1998 ).
24.
Close up, the granite is a coarse-grained rock consisting of large ( 2 5 cm ) white or pink feldspar crystals, glassy brown quartz and flakes of black mica, and containing inclusions of dark Malmesbury hornfels.
25.
MARS _ Photos of deep beds of sedimentary rock on Mars suggest that the Red Planet was once a planet of lakes, with water seeping into craters and helping to form layer upon layer of fine-grained rock.
26.
Along the lower shore the coarse grained rocks are partly covered by brown seaweeds such as Flat wrack " ( Fucus spiralis ) " and Knotted wrack " Ascophyllum nodosum ", while pools and crevices in the rocks provide shelter for a wide variety of algal species, such as the red seaweed " Corallina officinalis ".
