Where to Find Chalcedony in Montana

Montana has 9 mapped collecting spots that report chalcedony, spread across 7 counties. The largest share sits in Big Horn County County with 2 spots. 9 of the spots are on land mapped as publicly accessible.

Spot list checked against source data on April 1, 2026.

Standout chalcedony spots in Montana

Hand-picked from the full list below, with the reason each one earns a trip.

Pryor Mountains
Big Horn County County
The Pryor Mountains stand out for Dryhead-style agate, with Mindat listing agate and chalcedony from the range and a named Dryhead Agate Mine in the Bighorn River area. The same Big Horn County country also carries fossil-bearing sedimentary units, so the locality needs careful land-status and fossil-rule checks rather than casual blanket collecting.
American Bar
Lewis and Clark County County
American Bar belongs to the upper Missouri River sapphire province, where GIA traces gem-quality sapphire mining back to 1865. The associated heavy-mineral suite, including cassiterite, garnet, kyanite, topaz, gold, and chalcedony, makes the Missouri River bars one of Montana's most mineralogically varied placer settings.
Yellowstone River (Billings area)
Yellowstone County County
The Billings reach of the Yellowstone River is a benchmark Montana agate setting, where river gravels carry chalcedony, jasper, chert, and dendritic moss agate. Mindat records agate from Yellowstone County, and regional visitor and BLM guidance both point collectors toward public-land surface collecting rather than quarry or fee-pit material.

Best counties for chalcedony in Montana

Ranked by the number of mapped chalcedony spots. County links open the full rockhounding page for that county.

Every chalcedony spot we track in Montana

Sorted by county. Coordinates open in Google Maps.

Spot	County	Minerals	Coordinates	Access
Big Horn CanyonRoute 211	Big Horn County	Agate Chalcedony Jasper Silicified Coral Fossils	45.3130, -107.9604	Public
Pryor MountainsBad Pass Road	Big Horn County	Fossils Agate Chalcedony Jasper Petrified Wood	45.2386, -108.2675	Public
Mount BlackmoreBlackmore Trail	Gallatin County	Agate Chalcedony Hyalite Opal Petrified Wood	45.4447, -111.0035	Public
American Bar	Lewis and Clark County	Sapphire Cassiterite Chalcedony Garnet Gold Kyanite Limonite Topaz	46.8131, -111.9292	Public
Missouri RiverDanas Point Drive	Lewis and Clark County	Cassiterite Chalcedony Garnet Gold Kyanite Limonite Sapphire Topaz	46.7284, -111.8746	Public
Jefferson RiverPrimrose Lane	Madison County	Agate Chalcedony Jasper Petrified Wood	45.6902, -112.2745	Public
MinerTom Miner Creek Road	Park County	Agate Chalcedony Jasper Petrified Wood	45.1918, -110.9271	Public
TerryBroadview Bench Road	Prairie County	Petrified Wood Chalcedony Jasper	46.7727, -105.2599	Public
Yellowstone River (Billings area)Highway 312	Yellowstone County	Montana Agate Chalcedony Chert Jasper	45.9054, -108.3174	Public

Before you go

Read the chalcedony identification guide so you know what a keeper looks like in the field: Chalcedony in the encyclopedia.

Chalcedony in Montana FAQ

Where can you find chalcedony in Montana?+

The mapped spots concentrate in Big Horn County County, Lewis and Clark County County, and Gallatin County County. Every spot on this page appears on the map above with coordinates and access notes.

How many chalcedony spots are mapped in Montana?+

9 spots across 7 counties. The RockHoundR app keeps the same spots on an offline map with public land overlays, geology layers, and your saved finds.

Is it legal to collect chalcedony in Montana?+

Hand collecting of common rocks and minerals in small amounts for personal use is generally allowed on BLM and U.S. Forest Service land, with limits set by the local field office. National parks, most state parks, and tribal land are closed to collecting. 9 of the 9 mapped spots here sit on land marked public. Always confirm current rules with the managing agency before you dig.

Where else to find chalcedony

More minerals to hunt in Montana

Hunt chalcedony in Montana with the map in your pocket

RockHoundR puts these spots on an offline map with BLM and Forest Service overlays, geology layers, and a log for your finds.