Contents
Page [Introduction] 5 [Properties of gemstones] 5 [Crystals] 7 [Cutting and polishing of gemstones] 10 [Cabochon gems] 10 [Faceted gems] 13 [Tumbled gems] 17 [Texas gemstones] 18 [Amber] 18 [Augite] 18 [Beryl] 18 [Celestite] 19 [Diamond] 19 [Epidote] 19 [Fluorite] 20 [Fossil wood] 20 [Gadolinite] 21 [Garnet] 22 [Jet] 22 [Labradorite] 23 [Microcline] 23 [Obsidian] 24 [Opal] 24 [Pearl] 24 [Quartz] 25 [Crystalline varieties] 25 [Amethyst] 25 [Citrine] 25 [Rock crystal] 26 [Rose quartz] 26 [Smoky quartz] 26 [Cryptocrystalline varieties] 27 [Chalcedony] 27 [Agate] 27 [Agatized wood] 27 [Carnelian] 27 [Jasper] 27 [Sanidine] 28 [Spinel] 28 [Tektite (bediasite)] 28 [Topaz] 29 [Tourmaline] 30 [Turquoise] 31 [Glossary] 32 [Selected references] 34 [Index] 41
Illustrations
Figures— Page [1. Typical crystal form of three common Texas gemstones] 9 [2. Variations of the cabochon cut] 10 [3. Diamond saw] 11 [4. Cabochon properly attached to dop-stick] 12 [5. Cabochons at various stages of cutting and polishing] 12 [6. Nomenclature of the standard American brilliant cut] 13 [7. Facet table] 14 [8. Grinding the table facet on a rough stone] 15 [9. Stone dopped to table facet] 15 [10. Preformed stone dopped to table facet] 16 [11. Proper sequence of cutting of the pavilion facets] 16 [12. Proper placing of pavilion girdle facets] 17 [13. Proper sequence of cutting of crown facets] 17 [14. Common crystal form of Travis County celestite] 19 [15. Common crystal form of fluorite] 20 [16. Crystal faces on microcline specimen shown in Plate III] 23 [17. Common crystal form of spinel] 28 [18. Crystal faces on topaz crystal shown in Plate V] 29 [19. Cross section through irregularly colored stone] 30 [20. Common crystal form of Llano County tourmaline] 31
Plates— Page [I. A, Gem-quality celestite crystals from Travis County. B, Opalized wood from the Texas Gulf Coastal Plain] 35 [II. A, Gem-quality garnet crystals and faceted gem from Gillespie County. B, Labradorite from Brewster County] 36 [III. A, Pink microcline crystal. B, Smoky quartz. Both from Burnet County] 37 [IV. Polished agate from gravels of the Rio Grande near Zapata, Zapata County] 38 [V. A, Texas tektites (bediasites). B, Topaz crystal from a pegmatite dike near Streeter, Mason County] 39 [VI. A, Topaz from stream gravels near Streeter, Mason County. B, Tourmaline crystals in schist from Llano County] 40
[Table 1. Properties of some common Texas gem minerals] 8
Texas Gemstones
ELBERT A. KING, JR.
INTRODUCTION
Throughout history man has sought stones and minerals for personal adornment and ornamentation. Stones and minerals that are sufficiently beautiful, durable, and rare are known as gemstones. A gemstone with only one of these qualities is less desirable than one with all three. For example, a stone with rich color but not sufficiently durable to withstand daily wear in rings finds little favor as a gemstone except in brooches or pins where the stone is relatively safe from abrasion. Likewise, a stone that is beautiful and durable may be of little interest as a gemstone because it is commonly found in great quantities. To be valued highly, gemstones must be beautiful to the eye, durable enough to withstand wear, and rare enough so that they are not easily obtained.