Fort Settlement map 5440 Elkins Road Sugar Land, TX 77479 (281) 634-6440. Garcia map 18550 Old Richmond Rd. Sugar Land, TX 77498 (281) 634-3160. Hodges Bend map 16510 Bissonnet Houston, TX 77083 (281) 634-3000. Lake Olympia map 3100 Lake Olympia Parkway Missouri City, TX 77459 (281) 634-3520. McAuliffe map 16650 South Post Oak Houston, TX 77053 (281) 634-3360. Missouri City map
Within the feldspar group, the plagioclase minerals are only differentiated from the potassium feldspars by the presence of parallel striations seen on some plagioclase cleavage surfaces. Potassium Feldspar:
Igneous rocks are classified according to their mineral content: 1  Ultramafic rocks are dominated by olivine and/or pyroxene. 2  Mafic rocks are dominated by plagioclase and pyroxene (even if you can't see them with the naked eye) and smaller amounts of olivine.Intermediate rocks are roughly even mixtures of felsic minerals (mainly plagioclase) and mafic minerals (mainly hornblende, pyroxene, and/or biotite).There is little or no quartz. Felsic rocks are mostly feldspar (especially K-feldspar), at least 10% quartz, and less than 15% mafic minerals (biotite, hornblende).afic rocks are dominated by plagioclase and pyroxene (even if you can't see them with the naked eye) and smaller amounts of olivine. Intermediate rocks are roughly even mixtures of felsic minerals (mainly plagioclase) and mafic minerals (mainly hornblende, pyroxene, and/or biotite).