Collection: Lithophysis
Lithophysis is an interesting geological structure found in certain types of volcanic rocks, particularly rhyolites .
🔍 Definition
The word lithophysis comes from the Greek lithos (stone) and physa (bubble, breath). It refers to a rounded or oval cavity present in certain volcanic rocks, generally partially or completely filled with crystals or secondary minerals.
🪨 Training
Lithophyses are formed during the cooling of acidic magma (rich in silica), particularly in rhyolites or obsidians . During cooling:
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Gas bubbles form in the still pasty lava.
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These bubbles become trapped in the solidifying rock.
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Over time, the gases escape or dissolve, leaving an empty cavity .
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The interior may then be lined or filled with quartz crystals , feldspar , zeolites , or other secondary minerals from circulating hydrothermal fluids.
🧬 Features
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Size : a few millimeters to several centimeters in diameter.
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Shape : Rounded, often with a concentric (like onion layers) or radial structure.
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Minerals present : quartz, tridymite, cristobalite, hematite, zeolites, etc.
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Appearance : sometimes spectacular, with beautiful internal crystallizations .
📍 Where can we find them?
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In pearlitic rhyolites of the United States (New Mexico, Colorado).
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In Iceland, in volcanic areas.
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In France: they can be observed in certain volcanic regions of the Massif Central.
🎨 Interest
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Scientific : they provide information on the conditions of lava solidification and on post-volcanic processes.
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Aesthetics : Some lithophyses are sought after for their crystalline beauty, sometimes used as collector's items or ornamental stones .
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