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Table of Contents


Problems in the European Literature about Agates. 4

Problems in the American Literature about Agates and Geodes. 5

The History of the Term “Cryptocrystalline”. 7

Agate versus Chalcedony. 8

Chert versus Flint 9

Cherts versus Agates. 9

The Agates in Lava Voids. 10

Silicate Mineral Reactions Forming Agates. 11

The Agates Formed as Nodules. 12

Ash as a Source of Agate Silica. 13

The Agates are Made of Clays. 14

Chlorite in Agates—a Clay Cousin. 16

Crystal Structures versus Morphologies. 17

Inclusions Show Agate Genesis. 18

The Agates and Inclusions as Rocks. 19

Geochemical Definitions of Agate, Jasper, and Opal 20

Carbonate as a Catalyst to Form Agate. 22

The Formation of Silica Gels. 23

Water for Agate Formation. 24

Hunting Agates Geologically. 25

Temperature and Time of Formation for Agates. 27

Depth of Burial Limit for Agates. 27

Temperature Ranges Forming Agates. 28

Lava Systems with Agates and Geodes. 30

Metamorphic Systems and Agates. 31

Banding with the Calcium-Silicates. 33

Epilogue. 34

Summary. 35


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