变质岩实习4 接触变质岩

1、实习4,接触变质岩,通过学习典型接触变质岩标本和薄片的实习,掌握其结构,构造等基本特征. 要求： 理解讲课内容, 掌握角岩结构, 斑状变晶结构; 描述手标本和薄片的的结构构造; 每个片子2个典型结构素描图; 掌握变质矿物红柱石和堇青石的鉴定特征. 实习样品： 红柱石角岩 堇青石角岩,Keys to identification are high relief, low birefringence and parallel extinction.,These views show square end views of a few small andalusite crystals in a s

2、late from Mariposa County, California. Just a hint of zoning, caused by carbonaceous inclusions, can be seen in the crystals. When the zoning is well deveoped and appears as a cross it is termed chiastolite. The field of view is about 2.5 mm.,These views show a twinned andalusite crystal, partially

3、altered to sericite. Andalusite that shows a cross in end view is termed chiastolite. The cross appears, in part, because of dark included organic matter. The field of view is about 3.5 mm.,Cross polarized light, 40 x,Plane polarized light, 40 x,Cordierite in a garnet-cordierite-biotite schist. Cord

4、ierite is colorless, and relief is similar to plagioclase feldspars and quartz, but it tends to be dustier than either of these other two minerals. Birefringence is up to 1st order white, like plagioclase and quartz, and can have polysynthetic twinning (center) that resembles plagioclase. Note that

5、there can be THREE directions of polysynthetic twinning, contrasting with none in quartz and typically two in feldspars.,This sample contains large twinned cordierite (left side) and a highly fracture garnet with some quartz inclusions (right side). Minor biotite and quartz are also present. The cordierite interference colors and twins, visible in the XP view, make this cordierite appear si