Mariposa (butterfly) Calcite, Santa Eulalia, Chihuahua, Mexico
Contributed by: Chris Clemens
minID: HVT-60K
Date: Apr 20th, 2026
Locality: West Camp, Santa Eulalia Mining District, Aquiles Serdán Municipality, Chihuahua, Mexico (See on Mindat)
Size: 79 x 32 x 101 mm
Weight: 272 g
Description:
Mariposa calcite shows bright orange fluorescence under short wave UV (254 nm) on the underside of the base of the piece. Note the fluorescent zoning. This fluorescent response is typical for this material.
Top side of same specimen showing the 2-generation crystal growth that is characteristic of mariposa calcite. The initial growth phase results in the formation of classic scalenohedral calcite crystals which are typically coated with a thin layer of iron oxide, giving them a red/brown-colored appearance. During the second phase of growth, the initial scalenohedral phase is overgrown with yellow/brown rhombohedral calcite, resulting in caramel-colored dogtooth crystals containing dark brown internal phantoms. Of interest to the fluorescent mineral collector, the first phase of scalenohedral calcite growth often shows a bright orange, fluorescent response under shortwave UV.
Originally posted by Chris Clemens on Nature's Rainbows in 2020.
Summary of luminescence responses:
Calcite (Mindat) (RRUFF)
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Red