rhombohedral: 46, 54 Clemens salt dome: 91 Coal Creek serpentine: 87, 88 Coke County: 20, 49 Coleman County: 86 color of minerals: 16 columns: 18 Comal County; 45, 69 Comanche County: 49 common opal: 78 composition of minerals: 99 concretions: 19 conglomerate: 11, 12, 41, 55, 81 gneiss: 59 contact metamorphism: 13 copper: 52, 59, 90 blue copper: 53 glance: 52 green copper carbonate: 53 minerals: 52 pyrites: 53 yellow copper ore: 53 coquina: 41, 69 Crane County: 66 Cretaceous: 2, 3, 20, 21, 45, 46, 49, 51, 55, 57, 60, 65, 68, 69, 70, 74, 75, 84, 86, 88 cryptocrystalline quartz: 81, 84 crystal, definition of: 14 crystals, twinned: 46, 63 crystalline minerals, definition of: 14 Crosby County: 79 crust, earth’s: 2 cubic cleavage: 17, 57, 65 Culberson County: 1, 45, 52, 53, 58, 59, 60, 65, 75, 79, 83, 90, 91, 95 D Daingerfield: 70 Dallas: 88 Damon Mound salt dome: 91 daughter elements: 95, 96 Davis Mountains: 45, 85, 98 Delaware Mountains: 65 diamond: 62 diatomaceous earth: 78 diatomite: 40, 78 Dickens County: 79, 98 Dietrich, John W.: vii dikes: 72, 79 dog-tooth spar: 46, 47 dolomite: 29, 30, 32, 36, 38, 40, 43, 54, 68, 75, 87, 88 dolomitic limestone: 68 Double Mountain Fork of the Brazos River: 43 double refraction: 46 dravite: 95 Duval County: 78, 83, 91, 97 dynamic metamorphism: 14 E Eagle Flat: 93 Eagle Mountains: 56, 57, 90, 95 earth’s crust: 2 east Texas: 70 Ector County: 79 Edwards Limestone: 68, 69, 84 effervescence in acid: 18 El Capitan Peak: 1 elements: 7, 8, 95, 96 Ellenburger strata: 55, 84 El Paso: 48, 58, 85, 88 El Paso County: 48, 58, 62 epoch: 2 era: 2 erosion: 11 extrusive igneous rocks, definition of: 9 F Fairland: 54 Falfurrias: 64 Fannett salt dome: 91 Fayette County: 52, 64, 84, 98 feldspar: 8, 29, 30, 31, 33, 34, 35, 37, 45, 51, 55, 59, 61, 72, 79, 80, 85, 86 albite: 55 amazonstone: 56 microline: 55, 56, 61 orthoclase: 55, 61 fibrous gypsum: 64, 65 filtering sand: 86 Fisher County: 20, 49, 58, 65 Flawn, Peter T.: vii flint: 84 flowstone: 18 flow structure: 85 fluorite: 29, 32, 34, 35, 37, 38, 56, 72 Foard County: 52, 58 foliation: 87 fool’s gold: 53, 80 formation: 6 Fort Bend County: 91 Fort Worth: 88 fracture of minerals: 17 fragmental rocks: 12 Franklin Mountains: 48, 58, 62, 85 Frasch method of sulfur mining: 91, 92 Fredonia: 67 Freer: 78, 83 furnace (_see_ blast furnace; open-hearth furnace)