Part 29

Period—a unit of geologic time, a subdivision of an era.

Permian—the last period of the Paleozoic Era (see p. 3).

Physiographic outline map—shows location of natural regions (p. 42).

Playa lake—a temporary shallow lake in a nearly level, closed basin, which has no drainage outlet.

Pleistocene—the first epoch of the Quaternary Period (see p. 3).

Pliocene—the last epoch of the Tertiary Period (see p. 3).

Precambrian—comprises the Early and the Late Precambrian Eras, the earliest great divisions of geologic time. Rocks that formed more than 600 million years ago are known as Precambrian rocks.

Pyritohedron—a solid that has twelve 5-sided faces.

Quaternary—the present period of geologic time; the second period of the Cenozoic Era (see p. 3).

Recent—the present epoch of geologic time; the second epoch of the Quaternary Period (see p. 3).

Sectile—describes material, such as soap, that can be cut smoothly with a knife.

Sediments—material deposited by water, wind, or ice on the earth’s surface.

Sedimentary rocks—rocks made up of sediments.

Series—a subdivision of a system that includes all rocks formed during an epoch.

Specific gravity—the ratio of the weight of a substance to the weight of an equal volume of water.

Streak—the color of the powder of a mineral.

System—all rocks formed during a period.

Tertiary—the first period of the Cenozoic Era (see p. 3).

Translucent—light will pass through, but objects cannot be seen.

Transparent—light will pass through, and objects can be seen.

Trans-Pecos—area of Texas located west of the Pecos River (see p. 42).

Volcanic rocks—igneous rocks that have formed on the earth’s surface; extrusive rocks.

Index

A acid: 18, 22 acid tests (see also chemical tests): 18 actinolite: 82 schist: 87 agate: 21, 83 agatized wood: 20, 84 age, earth’s crust: 2 alabaster: 65 albite: 55 alkali lakes: 66, 83 Allamoore: 87, 93 alloys: 52 almandite: 58 Alpine: 57, 78, 82, 90 Altuda Mountain: 57, 90 amalgam: 51 amazonstone: 56 amethyst: 37, 82 Amethyst Hill: 82 amorphous minerals, definition of: 15 amphibole asbestos: 29, 33, 34, 44 Anderson County: 70 Andrews County: 83 Angelina County: 52 anhydrite: 28, 29, 30, 35, 36, 43, 65, 66, 91 anthophyllite: 93 antigorite: 87 Apache Mountains: 65 apatite: 72 Archer County: 52 argentite: 26, 27, 89, 90 argentiferous galena: 57, 90 Armstrong County: 79 asbestos: 43 amphibole: 29, 33, 34, 44 chrysotile: 44, 87 ash, volcanic: 41, 97 augite: 45 Austin: 46, 62 autunite: 97 azurite: 35, 52, 53, 54

B Babyhead: 72 Balcones fault zone: 10, 42, 45, 88 Bandera County: 45 Baringer Hill pegmatite: 80 barite: 15, 28, 31, 32, 35, 36, 38, 44, 48 barium: 45 Barrilla Mountains: 85 Baylor County: 45, 52, 98 basal cleavage: 76, 93, 94 basalt: 40, 41, 45 basement: 2, 9 Bastrop County: 64 Bell County: 69 bentonite: 51, 52 beryllium: 80 Big Bend area: 9, 42, 51, 75, 77 Big Branch Gneiss: 59 biotite: 32, 33, 34, 76 Bird mine: 90 Blanco County: 44, 58, 59, 61, 70, 83, 87, 94 black mica (see biotite) blast furnace: 70, 71 blast sand: 86 bleaching clay: 51 blue copper: 53 Boerne: 18 Boling salt dome: 91 books about rocks and minerals: 24, 39, 100 brass: 52 braunite: 26, 27, 73 Brazoria County: 91 Brazos County: 98 Brazos River, Double Mountain Fork and Salt Fork of: 43 breccia: 12, 41, 81 Brewster County: 45, 46, 47, 49, 50, 57, 65, 70, 76, 77, 78, 82, 84, 85, 90 brimstone: 90 bronze: 52 Brooks County: 64 Brown, Thomas E.: vii Brown County: 45, 49 brown iron ore (see also limonite): 70 Bryan Mound salt dome: 91 building sand: 85 Burnet: 56, 80, 97 Burnet County: 18, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 70, 76, 79, 80, 81, 82, 83, 97

C calcareous sinter and tufa: 46 calcite: 7, 14, 18, 19, 20, 21, 28, 30, 31, 32, 34, 35, 36, 38, 45, 46, 49, 50, 51, 54, 56, 64, 68, 75, 86, 87, 88, 91 dog-tooth spar: 46, 47 Caldwell County: 88 caliche: 46, 47 Cambrian: 2, 3, 55, 58, 69, 86 Cameron County: 66 Capitan reef limestone: 1 Capitol building, Texas State: 62 cap-rock: 91, 92 carats: 60 carbon: 62, 63 carbonized wood: 20 carnotite: 30, 95, 97 Carrizo Mountains: 67, 83, 95 Casey, Miss Josephine: vii Cass County: 70 cassiterite: 27, 32, 47 Castile Gypsum: 91 Catahoula strata: 78, 86, 97 cave deposits: 18 caves: 18, 19, 49 Caverns of Sonora: 19 Cedar Lake: 83 Cedar Park: 70 celestite: 20, 28, 30, 35, 38, 48 cementing materials: 12, 46, 67, 70, 86 cerargyrite: 28, 29, 34, 37, 89, 90 cerium: 80 chalcedony (see also agate): 16, 21, 45, 78, 81, 83, 86 chalcocite: 21, 26, 27, 52, 54, 73, 89 chalcopyrite: 26, 52, 53, 54, 60 chalk: 40, 69 chemical elements: 7 chemical sediments: 12 chemical tests: 18, 43, 46, 47, 49, 52, 53, 54, 64, 68, 75 Cherokee County: 70 chert: 19, 40, 81, 84 chessylite: 53 china clay: 51 Chinati Mountains: 45, 57, 62, 85 Chisos Mountains: 45, 62, 85 chlorite: 93 schist: 87 chrysotile: 44, 87, 88 asbestos: 44, 87 cinnabar: 36, 49 clastic rocks: 12 clay: 40, 45, 49, 51, 70, 86, 88, 91 bentonite: 45, 51, 52 bleaching clay: 51 china clay: 51 kaolin: 51 clay minerals: 51 Clay County: 52 Clear Creek area: 63 cleavage: 17 basal: 76, 93, 94 cubic: 17, 57, 65 octahedral: 56, 57 pyramidal: 74 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