Coldwater Agate is a variety of chalcedony found primarily in the Coldwater Formation of Michigan, often occurring as nodules within sedimentary rock. Collectors prize these for their subtle banding and earthy colors, which are best revealed after being tumbled or slabbed for lapidary work.
Is this coldwater agate?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch coldwater agate with a known reference. Coldwater Agate sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Coldwater Agate leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Coldwater Agate typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: gray, white, yellow, orange, red, brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: nodular.
Often confused with
Coldwater Agate vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads vitreous on Coldwater Agate and waxy on Flint Nodules.
How to tell apart: Luster reads vitreous on Coldwater Agate and waxy on Chalcedony.
How to tell apart: Luster reads vitreous on Coldwater Agate and waxy on Jasper.
Often found alongside coldwater agate
Minerals reported to co-occur with coldwater agate. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.7 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Nodular
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Sedimentary
- Typical price
- $5-50 for typical specimens
Where rockhounds find coldwater agate
3 mapped spotsClassic worldwide localities
- Michigan, USA
- Ontario, Canada
- Lake Huron Basin
Field-hunting tip
Look in sedimentary country — that is the host setting where coldwater agate typically forms. If you start seeing calcite, dolomite, quartz in float, you are in the right ground. Field specimens usually show a nodular habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Iowa — start trip planning there.
Common questions
How do you identify coldwater agate?+
Where is coldwater agate found?+
Can I find coldwater agate in the United States?+
How much is coldwater agate worth?+
What rocks look like coldwater agate?+
What minerals are found with coldwater agate?+
What kind of rock does coldwater agate form in?+
What is coldwater agate used for?+
Find coldwater agate on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
