Where is Conglomerate with Chalcedony found?
Conglomerate (sedimentary rock) with cryptocrystalline quartz (chalcedony)
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Open the appConglomerate with Chalcedony occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Conglomerate with Chalcedony
United States
Various locations, including the Lake Superior region (e.g., 'Puddingstone' conglomerates), parts of the Southwest (e.g., Arizona, New Mexico) where silicification is common in sedimentary basins, and areas with ancient river systems.
United Kingdom
Known occurrences of 'Puddingstone' (Hertfordshire Puddingstone) which is a chalcedony-cemented conglomerate, particularly in southeastern England.
Australia
Found in various sedimentary basins, particularly where silicification processes have been active, often associated with ancient river channels or paleosols.
Brazil
Occurrences in regions with extensive sedimentary sequences and hydrothermal activity, leading to silicification.
Collecting tips
- Look for Coarse Sediments. Focus on areas with ancient or modern riverbeds, alluvial fans, or beach deposits where conglomerates are likely to form. Look for outcrops or stream beds containing rounded pebbles and cobbles.
- Examine Cementation. Once a conglomerate is found, inspect the matrix between the clasts. Chalcedony cement will often appear waxy, dull, or slightly translucent, and will be harder than typical carbonate or clay cements. It will scratch glass.
- Check for Hardness. Test the hardness of the cement. Chalcedony has a Mohs hardness of 6.5-7, so it will scratch steel and glass. This distinguishes it from softer cements like calcite.
- Observe Color and Texture Contrast. The distinct contrast between the varied clast colors and the often lighter or translucent chalcedony cement can be a good indicator. Look for a 'pudding-like' appearance.
Quick Check
- Color:
- Variable (clasts) with white, gray, blue, brown, or reddish (chalcedony cement)
- Luster:
- Waxy to dull (chalcedony cement), variable (clasts)
- Streak:
- White (for chalcedony cement; clasts will have their own streak or no streak)
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