Empire Mine: Purple Fluorite Rockhounding in Custer County, Idaho

Quick details

Access

Public area

County

Custer County

State

Idaho

Nearest road

National Forest Development Road 496

Coordinates

43.89248, -113.67015

Geology at Empire Mine

This spot sits on White Knob Limestone, mapped as limestone;conglomerate;sandstone;siltstone;mudstone that formed roughly 360 to 325 million years ago. Carbonate rock like this is the classic host for lead, zinc, and fluorite mineralization, which typically follows old cavities and replacement zones.

Mapped unit

White Knob Limestone

Age

360–325 Ma (Early Mississippian to Late Mississippian)

Rock types

limestone;conglomerate;sandstone;siltstone;mudstone

Elevation

7,450 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Best time to visit Empire Mine

Best months: April to October. Typical highs run 78°F in midsummer and 24°F in midwinter, with winter lows near 3°F. At about 7,450 ft, snow can block access from late fall well into spring, so check conditions outside of summer.

Climate normals: NOAA 1991-2020 monthlies, MACKAY LOST RVR RS station (3 mi away), adjusted for elevation.

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

State guidance last verified: April 1, 2026

• Idaho Panhandle National Forests, Emerald Creek
• Idaho Geological Survey
• Spencer Opal Mines (fee-dig operator)
• Community submissions reviewed against published agency rules

Found at Empire Mine

Each chip opens all spots that produce that material; the encyclopedia link opens the full ID and field guide.

• Purple FluoriteEncyclopedia →