sedimentary
Dragon Stone
Ohko Stone (Argillaceous sedimentary rock)
Hardness: 3-4 (Mohs scale), Color: Brown, tan, reddish-yellow, Luster: Earthy/dull, Crystal structure: Amorphous/clay minerals, Cleavage: None (irregular/jagged fracturing), Specific gravity: Variable due to porosity
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Brown, tan, reddish-yellow, Luster: Earthy/dull, Crystal structure: Amorphous/clay minerals, Cleavage: None (irregular/jagged fracturing), Specific gravity: Variable due to porosity
Formation & geological history
Formed through the accumulation of organic clay and silt in ancient riverbeds or lakes. The unique crater-like texture is the result of millions of years of water erosion and pressure, which creates deep nooks and crannies in the clay-based substrate.
Uses & applications
Primarily used in aquascaping (aquarium landscaping) for its unique aesthetic and inert properties, also used as decorative garden stone and in reptile enclosures.
Geological facts
Dragon stone is popular because it is chemically inert and does not affect the pH or water hardness of an aquarium, unlike many other crater-textured rocks like limestone or fossilized coral.
Field identification & locations
Identify by its 'dragon scale' texture with numerous deep indentations and holes. It is commonly found in the coastlines of Japan and the UK. For collectors, it is fragile and should be handled with care as it is clay-based and can crumble if dropped.
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