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:
Porphyritic volcanic rocks are further classified by phenocryst type using mineral name modifiers given in the order of decreasing abundance. The term phenocryst is used for a crystal that is significantly larger than the average size of the groundmass crystals; in practice, these are generally >~1 mm. Thus, olivine-plagioclase phyric basalt contains >10% phenocrysts, the dominant phenocryst being olivine, with lesser amounts of plagioclase.