Calcite and Dolomite from the Sweetwater Mine, Reynolds County, Missouri
Contributed by: Michael Crawford
Date: Sep 22nd, 2025
Locality: Sweetwater Mine, Ellington, Reynolds County, Missouri, USA (See on Mindat)
Size: 10 x 13 cm
Description:
This is a calcite and dolomite specimen from the Sweetwater Mine, Ellington, Reynolds County, Missouri. It features translucent, prismatic scalenohedral crystals of calcite that have bright magenta fluorescence under midwave UV illumination. The calcite fluorescence is a dimmer red color under longwave and shortwave illumination.
The calcite crystals formed on a coating of small rhombic dolomite crystals. The dolomite crystals are about 2 mm and fluoresce white under longwave illumination. The dolomite fluorescence is dimmer under midwave and shortwave light. The longwave fluorescence reveals zoning in the dolomite crystals. The zoning is shown in the closeup image.
The shortwave emission spectrum of the calcite has a peak in the ultraviolet region with a maximum at 350 nm. This peak is activated by cerium replacing calcium. The midwave magenta fluorescence is from the blue shoulder of ultraviolet fluorescence from the cerium activation combined with the red fluorescence from manganese activation. The red midwave fluorescence has a broad peak with a maximum at 610 nm. The red longwave fluorescence is also caused by manganese activation.
The longwave fluorescence of dolomite is activated by organics. The white fluorescence has a maximum at 435 nm.
Summary of luminescence responses:
Calcite (Mindat) (RRUFF)
- Fluorescence under Midwave (305nm LED) UV light: Pink
- Fluorescence under Shortwave (255nm LED) UV light: Red
- Fluorescence under Longwave (365nm LED) UV light: Red
- Fluorescence under Longwave (365nm LED) UV light: White