Texas Gemstones

Tektite (Bediasite)

Composition: A natural glass, approximately 75% SiO₂, 15% Al₂O₃, 4% FeO, also MgO, Na₂O, K₂O, and traces of other elements. Crystal structure: amorphous. Hardness: 5 to 6. Specific gravity: 2.33 to 2.44. Luster: vitreous, often dull on weathered surfaces. Color: dark brown, greenish brown, appears black in thick sections. Streak: uncolored. Cleavage: none. Fracture: conchoidal. Tenacity: brittle. Diaphaneity: transparent to subtransparent. Refractive index: 1.488 to 1.512.

The average bediasite size is about 1 inch in diameter, although specimens approximately 3 inches in diameter are known. The uncut tektites are very interesting, showing a variety of shapes and surface features (Pl. V, A) and many exhibit contorted flow structure. The surface of many tektites is grooved or furrowed, while on others it is smooth or frosted. The Texas tektites are known as “bediasites,” after place names in Grimes County traceable to the Bedias Indians who formerly lived there.

Dark brown and greenish-brown tektites have been found in Texas in gravels at scattered localities in Walker, Grimes, Brazos, Burleson, Lee, Fayette, Gonzales, Lavaca, and DeWitt counties. Outside of Texas the only other authenticated tektite localities in the United States at the present time are in Dodge and Irwin counties, Georgia. A fragment of a similar tektite has recently been reported from near Martha’s Vineyard, Massachusetts. The tektites reported from Oklahoma are now known to be pebbles of obsidian.

Although tektites have little value or beauty as gemstones, they have been cut by lapidaries as both faceted and cabochon stones. Tektites take a high polish but are mostly so dark in color that they appear black.

The origin of tektites is of great scientific interest and is currently the subject of much debate. Some scientists believe that tektites are of meteoritic origin, while others believe that tektites were formed by various terrestrial processes. Since no one has actually observed a tektite to fall or form, and many of the theories of origin are difficult to prove without direct observation, the origin of tektites is likely to remain in controversy for some time.

Topaz

Composition: Al₂(F, OH)₂SiO₄. Crystal system: orthorhombic. Hardness: 8. Specific gravity: 3.4 to 3.6. Luster: vitreous. Color: pale blue, sky blue, greenish, white, wine yellow, straw yellow, grayish, pink, reddish, and orange. Streak: uncolored. Cleavage: one direction, basal, highly perfect. Fracture: conchoidal to uneven. Tenacity: brittle. Diaphaneity: transparent to subtranslucent. Refractive index: about 1.60 to 1.63. Dispersion: moderate.

Various yellow and smoky colored quartz gems are offered for sale as “Spanish Topaz,” “Smoky Topaz,” “Madeira Topaz,” and “Topaz Quartz.” These names are entirely misleading and should be dropped from usage.

Fine gem-quality white, pale-blue, and sky-blue topaz has been found near Streeter, Grit, and Katemcy, Mason County. This Texas gem material compares favorably in color, size, and clarity with topaz found anywhere in the United States. Fine crystals of topaz (Pl. V, B, and fig. 18) occasionally are found in pegmatite dikes associated with quartz, black tourmaline, cassiterite, and pink microcline. Many of the gem-bearing pegmatites have been eroded away, leaving the topaz concentrated in the stream beds. The stones mostly occur as frosted, stream-worn pebbles (Pl. VI, A) in the numerous small creeks in the area. The topaz is heavier than the quartz and microcline that compose the stream gravel and is commonly found immediately on top of the granite bed-rock in the bottom of the stream bed. The stones tend to lodge behind boulders or small dikes cutting across the stream.

The white or colorless stones are by far the most common, outnumbering the bluish stones about ten to one. The color of the blue stones tends to be irregularly distributed in zones parallel to the crystal faces. Topaz that is colored in this manner should be cut with the best blue color near the bottom or culet of the gem (fig. 19). If done correctly, this will give the entire gemstone the desirable blue color.

COLORLESS

BLUE

The colorless stones can be turned pale yellow, yellowish brown, or straw yellow by exposure to X-ray radiation, and some of the bluish stones will fluoresce faintly yellowish under ultra-violet light.

The largest gem-quality topaz crystal yet found in North America has come from Mason County. It is a pale-blue crystal weighing 1,296 grams, now in the collection of the U.S. National Museum. Several other large pieces, some weighing over a pound, have been found. One large crystal, exact weight unknown, was found near Katemcy. Several gem cutters have estimated that this stone could easily yield a single, flawless pale-blue gem of about 500 carats. Many large gems have been cut from topaz found in this area, including at least one stone of over 300 carats.

One obstacle in the cutting of topaz is its perfect basal cleavage. The gemstone should be oriented so that no facet of the stone will be parallel to or within less than about 5 degrees of the cleavage direction, or the facet may be very difficult or impossible to polish.

It is difficult to estimate the productivity of this area since its discovery in the early 1900’s. Few systematic attempts have been made to exploit the deposits, and a great amount of the topaz thus far recovered has been found by private collectors. The Mason County topaz deposits are still very productive, and additional exploration may uncover even more gem-producing areas.

Topaz has also been found in stream gravels or pegmatites in Burnet, Llano, Gillespie, and El Paso counties but very rarely in gem quality.

Tourmaline

Composition: H₉Al₃(B·OH)₂Si₄O₁₉; hydrogen often replaced by iron, magnesium, calcium, or fluorine. Crystal system: hexagonal. Hardness: 7 to 7.5. Specific gravity: 2.98 to 3.20. Luster: vitreous to resinous. Color: black, brownish black, brown, blue, green, red, pink, yellow, and gray. Streak: uncolored. Cleavage: two directions, very imperfect. Fracture: subconchoidal to uneven. Tenacity: brittle. Diaphaneity: transparent to opaque. Refractive index: about 1.62 to 1.64.

Black tourmaline is schorl; brown tourmaline, dravite.

Good crystals of black and dark brown tourmaline occur at Town Mountain near Llano, Llano County. The tourmaline crystals average about 1 inch in length, do not commonly exceed 2 inches, and are associated with white vein quartz. The quartz completely encloses the tourmaline, but the crystals can be broken free or the quartz can be trimmed away with the use of a diamond saw. The latter procedure is recommended whenever possible, for it is very easy to shatter the tourmaline crystals while trying to remove them from the quartz by other means. Many of the crystals are completely unsuitable for cutting, being too brittle or too badly cracked and flawed. However, some small crystals have been found that are of sufficient quality and size to yield flawless stones of a few carats. Few of these stones have been cut since the tourmaline is so dark that it appears opaque, and few persons find a gem of this nature attractive.

Good black and dark brown crystals of tourmaline associated with andalusite and graphite occur in the Packsaddle schist (Precambrian) near Sunrise Beach, Llano County (Pl. VI, B, and fig. 20). Although generally smaller in diameter than the crystals found at Town Mountain, they commonly exceed 3 inches in length, although the average size is a little over 1 inch. Many of these crystals are suitable for cutting into opaque or nearly opaque stones of about 5 or 6 carats.

Black tourmaline has also been found in Hudspeth and Culberson counties but not of sufficient quality to be used as a gemstone.

Turquoise

Composition: hydrous phosphate of aluminum and copper. Crystal system: triclinic. Hardness: 5 to 6. Specific gravity: variable, 2.6 to about 2.8. Luster: dull, sometimes waxy. Color: sky blue to greenish blue. Streak: white to greenish. Cleavage: none in massive material, two directions in crystals. Fracture: conchoidal to subconchoidal. Tenacity: brittle. Diaphaneity: subtranslucent to opaque. Refractive index: 1.61 to 1.65.

Turquoise of good sky-blue to greenish-blue color has been found a few miles southwest of Van Horn, Culberson County. Several shallow pits were dug at this locality about 1910; however, the amount of turquoise produced was small. The main occurrence of the turquoise was in seams about 1 millimeter thick along joints in the fine-grained rocks of this area. Persons who have visited Culberson County more recently report that even minute traces of the turquoise are now difficult to find at the old prospect pits. However, further prospecting in the area might yield some additional localities.

Small amounts of turquoise have been reported near El Paso, El Paso County, and also in volcanic rocks near the Jeff Davis-Brewster County line, north of Alpine.

A small amount of turquoise has been mined from several localities a few miles northwest of Sierra Blanca in the Sierra Blanca Mountains of Hudspeth County.

GLOSSARY

Amorphous—without definite molecular structure; not crystalline.

Baroque stone—an irregularly shaped, polished stone; usually applied to tumbled stones.

Baroque pearl—an irregularly shaped pearl.

Brilliancy—reflecting much light; having brightness.

Brilliant cut—a mode of arrangement of facets commonly used on round or oval stones. The standard American brilliant cut has 57 or 58 facets. Most diamonds of 5 or less carats are cut in this manner.

Cabochon—a stone cut with a flat or convex upper surface; sometimes faceted in part. Opal, star sapphire, and agate are stones that are frequently cut in this style (fig. 2).

Cambrian—a division of geologic time, estimated to be the time from 550 to 440 million years ago; the oldest time division of the Paleozoic era.

Carat—a unit of weight equal to ⅕ of a gram or 0.2 gram. One ounce avoirdupois is equal to 141.75 carats.

Cleavage—the tendency of certain minerals to split in particular directions yielding relatively smooth plane surfaces.

Conchiolin—an organic albuminoid substance found in pearls.

Conchoidal—a type of fracture having curved concavities or the approximate shape of one-half of a bivalve shell. Glass has excellent conchoidal fracture.

Cretaceous—a division of geologic time, estimated to be the time from 135 to 60 million years ago; youngest division of the Mesozoic era.

Crown—that portion of a faceted gem above the girdle; the upper portion of a facet-cut gem (fig. 6).

Cryptocrystalline—composed of very fine or microscopic crystals.

Crystal—the regular polyhedral form, bounded by plane surfaces, that is assumed by a mineral under suitable conditions. Crystals have definite external symmetry and internal molecular order.

Crystalline—possessing definite internal molecular order; not amorphous.

Cubic—in the general shape of a cube. The isometric crystal system is often called the cubic system.

Culet—the very bottom portion of a faceted gem; the point or line formed by the intersection of the lowest pavilion facets (fig. 6).

Dendritic—branching or tree-like in form.

Diaphaneity—relative transparency. The diaphaneity of a mineral is described as transparent, translucent, opaque, etc.

Dike—a tabular rock body, usually igneous in origin, which cuts across the surrounding rock strata.

Dispersion—a measure of the ability of gemstones to separate complex or white light into its component colors; often illustrated with a prism. Gemstones that are capable of separating colors of light widely are said to have high dispersion; gemstones not so capable of separating white light into colors are said to have low dispersion.

Dopping—the act of cementing a gemstone, either rough or partly finished, to a dop-stick.

Dop-stick—the wooden stick or cylindrical piece of metal to which a gemstone is cemented to facilitate handling during cutting and polishing.

Dop-wax—the agent or cement used to secure a gemstone to a dop-stick.

Emerald cut—a rectangular or square faceted stone with beveled corners whose surfaces are covered with several series of rectangular facets.

Eocene—a division of geologic time, estimated to be the time from 50 to 40 million years ago; one of the older divisions of the Cenozoic era.

Extrusive rock—igneous rock that has been extruded or forced out onto the earth’s surface.

Facet—a single plane polished surface on a faceted gem.

Facet head—a device used in the cutting and polishing of faceted gems; used to control the placement of facets and their relative angles (fig. 7).

Facet table—the equipment used in the cutting and polishing of faceted gems and the table on which most of the equipment is mounted (fig. 7).

Feldspar—a group of closely related silicate minerals including orthoclase, microcline, sanidine, plagioclase, labradorite, and others.

Fire—the reflections of variously colored light from a precious opal; also the different colors of light reflected from a faceted gem owing to the dispersion of the mineral.

Fracture—the texture of a freshly broken surface other than a cleavage surface, described as conchoidal, even, splintery, etc.

Gem—a cut and polished gemstone.

Gemology—the science dealing with the study of gemstones.

Gemstone—a mineral suitable for cutting into a gem; the term gemstones is frequently used collectively to include both cut and polished stones and rough stones.

Geode—a rounded or spherical rock cavity; commonly lined with crystals.

Girdle—the portion of a faceted gem separating the crown from the pavilion; the girdle may or may not be polished and usually contains about 2 percent of the total depth of the gem (fig. 6).

Gneiss—a coarse-grained metamorphic rock having segregations of granular and platy minerals that give it a more or less banded appearance without well-developed schistosity.

Grain (pearl grain)—a unit of weight equal to 0.05 gram or 0.25 carat; not the same as the Troy grain.

Granite—a granular igneous rock composed mostly of quartz, feldspar, and commonly mica and/or hornblende.

Hexagonal—having six angles and six sides; a crystal system in which the crystal faces are referred to four intersecting axes; three of these axes are equal, lie in the same plane, and intersect at angles of 60 degrees; the fourth axis is perpendicular to the other three.

Igneous rock—rock formed by solidification from a hot melt.

Index of refraction—a measure of the relative ability of a gemstone to “bend” incident light rays; sine of the angle of incidence of a light ray divided by the sine of the angle of refraction.

Intrusive rock—rock that has been pushed (usually in a molten state) among pre-existing rock strata, commonly along faults or fissures. Intrusive rocks do not reach the earth’s surface but are commonly exposed at the surface by later erosion.

Isometric—a crystal system in which the crystal faces are referred to three equal intersecting axes at right angles to each other.

Lap—a disc-shaped piece of metal or other material which is impregnated with diamond dust, or some other cutting or polishing agent, that is revolved while the gemstone is worked against it.

Lap plate—a metal plate to which a cutting or polishing lap is attached, usually by means of a threaded bolt and wing nut. The lap plate is attached to the shaft which is turned by the motor under the facet table.

Lapidary—one who practices the lapidary arts; a gem cutter.

Limestone—a sedimentary rock composed mostly of calcium carbonate.

Luster—the appearance of the freshly broken or unweathered surface of a mineral in reflected light (p. 5).

Main facet—as applied to the standard American brilliant cut, one of the first eight facets cut on either the crown or pavilion of a gem (fig. 6).

Matrix—the material in which a specific mineral is embedded; also the rock to which one end of a crystal is attached.

Metamorphic rock—rock that has been changed from its original state by heat, pressure, chemical action, or some combination of these factors.

Millimeter—¹/₁₀ centimeter; approximately ¹/₂₅ inch.

Mineralogy—the science concerned with the study of minerals, including their occurrence, composition, forms, properties, and structure.

Monoclinic—a crystal system in which the crystal faces are described in relation to three intersecting unequal axes, two of which are at right angles and the third inclined.

Oligocene—a division of geologic time, estimated to be the time from 40 to 28 million years ago; part of the Cenozoic era.

Opaque—does not transmit light.

Orbicular—containing orbs or spherical or eye-like markings or structures.

Orthorhombic—a crystal system in which crystal faces are referred to three unequal intersecting axes at right angles.

Pavilion—the portion of a faceted gem below the girdle (fig. 6).

Pegmatite—a body of coarse-grained intrusive igneous rock, commonly lens or dike shaped.

Perthitic—a plaid-patterned structure resulting from intermixture of soda- and potash-rich feldspars.

Phantom crystal—a crystal outline seen within another crystal, mostly due to entrapping of inclusions during the crystal’s growth.

Pleochroism—the property of transmitting different colors of light in different crystallographic directions.

Point—a unit of weight equal to ¹/₁₀₀ (0.01) carat.

Porous—containing pores or void spaces.

Precambrian—a division of geologic time, estimated to be all of geologic time prior to 550 million years ago; the time before the Paleozoic era.

Preform—a gemstone that has been ground to a rough outline of the finished shape of a gem.

Rhyolite—a fine-grained extrusive or shallow intrusive igneous rock of approximately the same composition as granite.

Rough—uncut, not worked by a lapidary, not cut and polished.

Schist—a metamorphic rock that contains an abundance of oriented platy minerals that enable the rock to be split with relative ease parallel to the flat surfaces of the platy minerals.

Silicified—replaced by or containing a large amount of quartz or silica.

Skill facet—a term often used for the pavilion girdle facets of the standard American brilliant cut (fig. 6).

Specific gravity—the weight in air divided by the loss of weight in water at a given temperature, or the weight of an object in air divided by the weight of an equal volume of water; also called relative density; the most commonly used standard temperature for this measurement is 4° C. or 39.2° F.

Star facet—one of the eight facets surrounding the table facet of a standard American brilliant cut (fig. 6).

Step cut—a mode of faceting in which the surface of the gem is covered by a series of square or rectangular facets; stones thusly cut are usually square, rectangular, or irregular with straight sides in outline.

Streak—the color of a mineral when finely powdered; usually determined by rubbing the mineral against a piece of unglazed porcelain.

Symmetry—the number, location, and balanced arrangement of crystal faces in reference to the crystallographic axes or other crystallographic planes or directions.

Synthetic gem—a gemstone manufactured by man that has approximately the same chemical composition and properties as a natural gemstone.

Table facet—the large horizontal facet found on the crown of many gems, often called simply the table (fig. 6).

Tenacity—the resistance of minerals to breakage, described by such terms as malleable, ductile, sectile, and brittle (p. 6).

Termination—the end of a crystal that is completely enclosed by crystal faces, the crystal end that is not attached to the matrix.

Tertiary—a division of geologic time, estimated to be the time from 60 to 1 million years ago; the Tertiary includes the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs (from oldest to youngest).

Tetragonal—having four angles; a crystal system in which the crystal faces are referred to three axes at right angles to each other, two of which are equal and the third longer or shorter.

Translucent—allowing the passage of light but diffusing it sufficiently so that objects on the other side cannot be clearly distinguished.

Transparent—clear, allowing free passage of light so that objects on the other side can be readily distinguished; opposite of opaque.

Triclinic—a crystal system in which the crystal faces are referred to three unequal axes, none of which are at right angles.

Tumbling—a process of polishing irregularly shaped gemstones (p. 17).

Vein—a tabular, irregular, or twisting mineral deposit that is thin in relation to its length and breadth, usually the result of solution or hydrothermal activity.

Vitreous—having luster, general appearance, or physical properties similar to glass.

Vug—an unfilled rock cavity, commonly lined with crystals; may later become filled by minerals owing to solution or hydrothermal activity.

SELECTED REFERENCES

Anderson, B. W. (1948) Gem testing: Emerson, New York.

Baker, C. L. (1935) Metallic and non-metallic minerals and ores (precious stones), in The geology of Texas, Vol. II, Structural and economic geology: Univ. Texas Bull. 3401, Jan. 1, 1934, pp. 568-569.

Barnes, V. E. (1940) North American tektites: Univ. Texas Pub. 3945, Dec. 1, 1939, pp. 477-582.

Dake, H. C., Fleener, F. L., and Wilson, B. H. (1938) Quartz family minerals: Whittlesey House, McGraw-Hill Book Company, Inc., New York.

Ford, W. E. (1932) A textbook of mineralogy (4th ed.): John Wiley and Sons, Inc., New York.

Kraus, E. H., and Slawson, C. B. (1947) Gems and gem materials (5th ed.): McGraw-Hill Book Company, Inc., New York.

Kunz, G. F. (1892) Gems and precious stones of North America (2d ed.): Scientific Publishing Company, New York.

Pough, F. H. (1953) A field guide to rocks and minerals: Houghton Mifflin Company, Boston.

Simpson, B. W. (1958) Gem trails of Texas: Granbury, Texas.

Sinkankas, John (1955) Gem cutting: D. Van Nostrand Company, Inc., Princeton, New Jersey.

—— (1959) Gemstones of North America: D. Van Nostrand Company, Inc., Princeton, New Jersey.

Smith, G. F. H. (1958) Gemstones (13th ed.), revised by F. C. Phillips: Methuen and Company, Ltd., London.

Sperisen, F. J. (1950) The art of the lapidary: The Bruce Publishing Company, Milwaukee, Wisconsin.

Sterrett, D. B. (1913) Gems and precious stones, in Mineral resources of the United States, Calendar Year 1912, Part II, Non-metals: U. S. Geol. Survey, pp. 1023-1060.

Plate I

Plate II

Plate III

Plate IV

Plate V

Plate VI

Index

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

actinolite: 26

agate: 20, 28, 38

agatized wood: 27

allanite: 21

almandite: 22

amazonite: 23

amazon stone: 23

amber: 18

amethyst: 25

Amethyst Hill: 25

amorphous gemstones: 9

andalusite: 30

Arkansas: 19

Armstrong County: 21

augite: 18, 28

B

Baringer Hill, Llano County: 21, 26

baroque pearls and/or stones: 17, 25

bediasite (tektite): 28-29, 39

beryl: 18

Big Bend National Park: 27

biotite: 23

Blanco County: 18, 22

Brazos County: 29

Brazos River: 25

Brewster County: 18, 23, 24, 25, 26, 27, 28, 31, 36

brilliancy: 5

brilliant cut, standard American: 13, 15, 16

Brown County: 19

Burleson County: 29

Burnet County: 20, 22, 23, 25, 26, 30, 37

C

cabochon gems: 10-12

Caddo Lake: 25

carbuncle: 22

carnelian: 27

cassiterite: 23, 29

celestite: 19, 35

chalcedony: 27

geodes: 26

chuck: 15, 17

citrine: 25-26

cleavage: 6, 13

coal: 22

Coke County: 19

color: 5

Colorado River: 25

Concho River: 25

crown girdle facets: 16, 17

crown of gemstone: 15, 16

crystals: 7-9

crystal systems: 7

crytolite: 21

Culberson County: 22, 23, 25, 26, 31

culet: 13

cutting and polishing: 10-17

cutting lap: 13

D

DeWitt County: 29

diamond: 19

saw: 10, 11

diaphaneity: 5

dispersion: 6

dopping: 12, 13

dop-stick: 12, 15, 17

dop-wax: 12, 15, 17

dravite: 30

durability: 6

Duval County: 21, 24

E

El Paso County: 22, 30, 31

emerald cut: 15

epidote: 19-20

F

facet, kinds of: 13

main: 16

skill: 16

table: 13, 14

faceted gems and/or stones: 10, 13-17

Fayette County: 20, 29

fergusonite: 21

fire: 5

Fisher County: 19

fluorite: 20, 21

Foard County: 19

fossil wood: 20-21, 22

fracture: 6

Franklin Mountains: 18

G

gadolinite: 21-22

garnet: 20, 22, 36

gemstones, by kinds: 18-31

geodes, celestite: 19

Georgia: 29

Gillespie County: 18, 22, 23, 25, 26, 30, 36

girdle facets: 16

gneiss: 22

Gonzales County: 20, 29

grain: 25

gram: 7

graphite: 30

Grimes County: 29

grinding: 12

Guadalupe River: 25

Gulf Coast: 25

Gulf Coastal Plain: 18, 20, 22, 35

H

hardness: 6

Hudspeth County: 18, 20, 22, 24, 25, 26, 27, 28, 31

I

index of refraction: 5

J

jasper: 27-28

Jeff Davis County: 26, 27, 28, 31

jet: 22

K

Kinney County: 28

L

labradorite: 23, 36

Lake Buchanan: 21

Lampasas County: 19

lap plate: 13

Lavaca County: 29

Lee County: 20, 29

lignite: 22

Live Oak County: 21

Llano County: 18, 19, 20, 21, 22, 23, 25, 26, 30, 31, 40

Llano River: 25

luster: 5

M

Madeira topaz: 29

Mason County: 20, 22, 23, 26, 29, 30, 39, 40

Massachusetts: 29

Maverick County: 18

microcline: 20, 21, 23-24, 29, 37

Mohs scale of hardness: 6

moonstone: 28

Mount Bonnell: 19

muscovite: 23

N

natural glass: 18, 24, 28

Needle Peak, Presidio County: 27

nivenite: 21

Nolan County: 19

Nueces River: 25

O

obsidian: 24, 29

Oklahoma: 29

opal: 20, 24

opalized wood: 35

orbicular jasper: 28

ounce: 7

P

Packsaddle Mountain: 23

Packsaddle schist: 30

palm wood: 21, 35

Palo Duro Canyon: 21

pavilion: 13, 16

facets: 16

girdle facets: 16, 17

pearl: 24-25

pegmatites and/or pegmatite dikes: 18, 20, 21, 22, 23, 26, 29, 39

petrified wood: 26

phantom crystals: 26

pistacite: 20

pleochroism: 5

point: 7

polishing: 17

lap: 13, 16

preformed stone: 16

preforming: 15

Presidio County: 20, 22, 24, 25, 26, 27, 28

properties of gemstones: 5-7

Q

quartz: 20, 21, 23, 25-28, 29, 30

smoky: 38

R

radioactive elements: 22

radioactivity of gadolinite: 21

rarity: 6

Reeves County: 26, 27

Rio Grande: 25

gravels of: 21, 27, 38

Valley: 27

rock crystal: 26

rose quartz: 26

S

Sabine River: 25

sanding: 12

sanidine: 28

sawing: 10

scheelite: 20

schorl: 30

size: 7

“skill” facets: 16

“slab” of gem materials: 11

Smithsonian Institution: 21

smoky quartz: 23, 26, 37

smoky topaz: 29

Spanish topaz: 29

specific gravity: 7

spinel: 18, 28

star facets: 17

step cut: 15

streak: 6

synthetic gems: 7

T

table facet: 13, 15

tektite (bediasite): 28-29, 39

tenacity: 6

thorogummite: 21

topaz: 23, 26, 29-30, 39, 40

quartz: 29

tourmaline: 26, 29, 30-31, 40

Town Mountain, Llano County: 26, 30

transparency: 6

Travis County: 19, 35

Trinity River: 25

tumbled gems: 17

turquoise: 31

U

U. S. National Museum: 30

V

value of gemstones: 6, 7

Val Verde County: 24

valverdites: 24

Van Horn, Hudspeth County: 27

W

Walker County: 29

Washington County: 20

Webb County: 21

weight, units of: 7, 25

Z

Zapata County: 38