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Dinosaur Bone Agate is a fossilized material where the original bone structure of dinosaurs has been replaced or permineralized by silica, primarily chalcedony. It is characterized by its distinctive cellular patterns, often referred to as 'cells' or 'webbing,' which are the preserved remnants of the bone's internal structure. The material exhibits a wide range of colors, often vibrant and variegated, making it a popular gemstone. While commonly called 'agate,' it is not a true agate in the geological sense (which forms in geodes or veins), but rather a pseudomorph after bone, where the silica has taken on agate-like banding or coloration.
How to Identify
- Color
- Extremely variable, ranging from black, gray, white, brown, tan, yellow, orange, red, pink, purple, blue, and green. Often multi-colored with distinct patterns.
- Luster
- Vitreous (glassy) to waxy.
- Texture
- Smooth when polished, but can feel slightly granular or porous on unpolished surfaces. The most distinguishing feature is the visible cellular structure of the original bone.
- Crystal Form
- Microcrystalline, typically chalcedony, filling and replacing the bone structure. No macroscopic crystal forms are present.
- Cleavage
- None, as it is a microcrystalline aggregate.
- Geological Environment
- Found in sedimentary rock formations where dinosaur remains were rapidly buried and subsequently exposed to silica-rich groundwater. Common in fluvial (river) and lacustrine (lake) deposits.
Key Facts
- Hardness: 6.5-7 on the Mohs scale (due to the chalcedony/quartz replacement).
- Specific Gravity: 2.58-2.64 (similar to quartz).
- Crystal System: Trigonal (for the constituent quartz/chalcedony, but the overall form is pseudomorphic after bone).
- Color: Wide range, including black, gray, white, brown, tan, yellow, orange, red, pink, purple, blue, green. Often variegated.
- Luster: Vitreous to waxy.
- Transparency: Opaque to translucent.
- Fracture: Conchoidal to uneven.
- Cleavage: None.
- Composition: Primarily silicon dioxide (SiO2) in the form of chalcedony, with trace impurities causing coloration. Original bone material (calcium phosphate) is largely replaced.
Quick Check
- Color: Highly variable, often multi-colored with distinct cellular patterns.
- Luster: Vitreous to waxy.
- Streak: White (due to chalcedony/quartz).
Physical Characteristics
- Crystal Habit: Pseudomorphic after bone; microcrystalline aggregate (chalcedony).
- Cleavage Type: None.
- Fracture Type: Conchoidal to uneven.
- Tenacity: Brittle.
- Luster Type: Vitreous to waxy.
Formation
Dinosaur bone agate forms through a process called permineralization and replacement. After a dinosaur dies, its bones are rapidly buried by sediment, protecting them from scavengers and decomposition. Groundwater rich in dissolved silica (SiO2) then infiltrates the porous bone structure. Over millions of years, the silica precipitates within the bone's cellular spaces (permineralization) and gradually replaces the original organic material and calcium phosphate (replacement). The silica often crystallizes as chalcedony (a microcrystalline variety of quartz), sometimes with banding patterns characteristic of agate, hence the 'agate' in its common name. The vibrant colors are due to trace minerals such as iron oxides (red, brown, yellow), manganese oxides (black), and chromium (green).
Usage
Primarily used as a lapidary material for cabochons, beads, carvings, and ornamental objects. It is highly prized by collectors and jewelers for its unique cellular patterns and vibrant colors. It also holds significant scientific value as a fossil, providing insights into ancient life.
Age Distribution
Mesozoic Era (Triassic, Jurassic, Cretaceous periods), approximately 252 to 66 million years ago.
Where to Find
Morrison Formation, Utah and Colorado, USA
One of the most famous sources, particularly for highly colorful and well-preserved gembone. The Morrison Formation is a sequence of Upper Jurassic sedimentary rocks.
Wyoming, USA
Various localities yield silicified dinosaur bone, often from Cretaceous formations.
Montana, USA
Known for dinosaur fossils, including silicified bone, from Cretaceous deposits.
Arizona, USA
While more famous for petrified wood, some dinosaur bone has also been found, particularly in Triassic formations.
Canada (Alberta)
Dinosaur Provincial Park and other areas are rich in dinosaur fossils, with some silicified bone occurrences.
Finding Tips
Research Localities
Identify specific geological formations known for dinosaur fossils and silicified bone. Public lands may have restrictions on fossil collecting.
Look for Bone Structure
Even unpolished, look for the characteristic porous or cellular texture that distinguishes bone from ordinary rock or wood. Weathered surfaces might reveal the internal structure.
Check for Hardness
Silicified bone will be hard (Mohs 6.5-7), unlike unmineralized bone which is much softer. It will scratch glass.
Observe Color and Luster
While variable, the vitreous to waxy luster and often vibrant, variegated colors can be indicative, especially when combined with bone structure.
Consult Experts
If unsure, consult with paleontologists, geologists, or experienced fossil collectors. Many areas require permits for fossil collection.
Similar Rocks
Petrified Wood
Silicified Wood
Also known as: Agatized Wood, Silicified Wood
Agate
Chalcedony (variety Agate)
Also known as: Banded Chalcedony
Jasper
Chalcedony (variety Jasper)
Also known as: Opaque Chalcedony
Scientific Classification
- Mineral Class
- Tectosilicate (as it is primarily quartz/chalcedony)
- Group
- Quartz Group
- Crystal System
- Trigonal (for the constituent quartz/chalcedony)
- Chemical Formula
- SiO2 (with trace impurities)
- Composition
- Silicon dioxide (chalcedony) replacing calcium phosphate bone material.
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