Rasmussenite

rasmussenite

phlogopite

stanevansite

lazaraskeite

Images

Formula: Ca(C2H3O3)2.3H2O
Hydrated organic compound, glycolate subgroup
Crystal system: Triclinic
Specific gravity: 1.53 measured, 1.55 calculated for the empirical formula
Hardness: 1
Colour: Colourless to white
Solubility: At room temperature, insoluble in water but slowly dissolves in dilute hydrochloric acid
Environments

Hydrothermal environments, organic mineral

Since the discovery of the first glycolate mineral, lazaraskeite, from the western end of Pusch Ridge in the Santa Catalina Mountains, Tucson, Arizona, USA, at least eight other glycolate minerals have been identified from the same locality, namely domitrovicite, fuchunite, glecklerite, jimkrieghite, lianbinite, puschridgeite, rasmussenite and stanevansite.
Rasmussenite is a new mineral, approved in 2024 and to date (September 2025) reported only from the type locality.

Localities

At the type locality, Western end, Pusch Ridge, Pima County, Arizona, USA, rasmussenite occurs in a heavily fractured leucogranite, 1 to 2 m below the rock surface. Associated minerals include chrysocolla, hematite, lazaraskeite, microcline, phlogopite, quartz and stanevansite. Rasmussenite is a secondary mineral believed to have formed through the interaction of fluids containing glycolic acid, C2H4O3 derived from decaying plant materials, plant root exudates, or bacterial activities with Ca produced by the alteration of primary and secondary minerals in the host rock.
Rasmussenite occurs as sprays or spherical aggregates of fibrous or acicular crystals, with individual crystals up to 0.30 x 0.01 x 0.01 mm3. It is colourless and transparent with a white streak and vitreous lustre (CJMP 2025).
Rasmussenite from the Pusch Ridge - Image

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