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Contents

Introduction. 5

Relationship between agate, chert, and quartzite. 7

Regional Agate Sites. 9

Regional Geology—The Black Hills. 10

Black Hills Agate Sites—Teepee Canyon. 14

Black Hills Agate Sites—S&G Canyon and Dewey Fault. 15

Black Hills Agate Sites—State Park Fault. 16

Regional Geology—The Ogallala Formation. 17

Regional Geology—The White River Group (Brule and Chadron). 19

Regional Geology—The Absaroka Volcanic Province. 21

Regional Geology—The Hartville Uplift. 22

Stratigraphic Profile—The Sharps Formation. 26

Stratigraphic Profile—The Brule Formation. 28

Stratigraphic Profile—The Chadron Formation. 30

Stratigraphic Profile—The Pierre Shale Formation. 35

Regional Geology—Stream Gravels. 37

Fairburn Region Chert-Agate Silica Inclusions and Structures. 39

Amygdules. 39

Bacterial mats, tubes. 40

Banding and Microsphere Structures in Fairburn Agates. 41

Black Mineralization. 45

Bone. 47

Bubblegum Agates (Bubblegum Cherts). 48

Calcite/Dolomite. 50

Chert Structures and Inclusions. 52

Chert Banding Center Formation. 54

Cristobalite—High Temperature Exposure. 57

Coral 58

Crinoids. 59

Echinoids (Sea Urchins). 59

Glauconite. 63

Gypsum.. 64

Oolitic Concentrations in Fairburn Cherts. 64

Pyrite/Pyrrhotite Mineralization. 70

Sponges. 73

Sponge Spicules. 74

Quartzite. 77

Radiolaria. 78

Red Jasper. 80

Stromatolites. 81

Sulfur Microspheres. 82

Yellow Jasper. 83

Volcanic Structures. 84

Scenic, South Dakota Black Agates. 88

Overview of the Fairburn Agate Geology. 91

General Conclusions on the Fairburns. 92

Candidate Fairburn Sources. 93

Confusion with the Fairburn Agates. 93

The Montana Dryhead Agates. 94

The Montana Dryhead Agate Inclusions and Structures. 100

Allophane. 100

Amethyst. 101

Anhydrite (Herringbone Anhydrite). 101

Apatite (Phosphate). 102

Calcite. 104

Hematite. 104

Hematite Grains. 105

Hemispheres. 105

Mordenite. 106

Quartz. 106

Sponge Spicules. 107

General Conclusions on the Dryheads. 107

Further Reading. 108

Kasper Jasper Press Titles. 109

 

 

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