Fossiliferous Chert or Agated Fossil Shell
Quartz var. Chalcedony replacement of fossil brachiopod/mollusk · Mineral Specimen / Fossil Specimen
Crystal System
Trigonal (Microcrystalline / Cryptocrystalline)
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2
Formation Process
Sedimentary / Replacement (Silicification / Diagenesis)
About This Crystal
An irregularly shaped, weathered brown nodule showing a hollow cavity with distinct, finely ribbed fossil impressions resembling a bivalve or brachiopod shell interior. The exterior matrix is brownish-tan with smooth, water-worn, and pitted textures, while the interior cavity exhibits a silky to dull vitreous luster over the intricate fossil ribs.
Physical Characteristics
Brown to tan body color, white streak, conchoidal fracture, specific gravity around 2.60 to 2.65, brittle tenacity, no notable cleavage due to microcrystalline structure.
Optical Properties
Subtranslucent to opaque, singly to aggregate anisotropic under cross-polarized light, no pleochroism.
Hardness & Durability
Origin Region
Worldwide, particularly common in sedimentary limestone and chert-bearing formations
Hardness & Durability
Mohs hardness of 6.5 to 7, high toughness due to microcrystalline interlocking quartz fibers, very stable.
Care & Maintenance
Wash with warm soapy water and a soft brush; highly resistant to chemicals except hydrofluoric acid; safe from normal sunlight fading.
Rarity & Value
Common to uncommon depending on the quality and clarity of the fossil preservation; value is primarily determined by paleontological interest and aesthetic appeal rather than gemstone value.
Special Characteristics
Contains natural fossil molds and casts (silicified fossils), showing exceptional preservation of fine biological structures within a microcrystalline quartz matrix.
Lore & History
Historically used as talismans and amulets by ancient cultures who viewed fossils as sacred stones or gifts from the earth; in modern metaphysical practices, fossils are associated with grounding, ancient wisdom, and connection to earth history.