TERRIUM — A mineralogy cabinet

Furcalita Laminar

Furcalita is a mineral with formula Ca₂(UO₂)₃O₂(PO₄)₂·7H₂O, in the Fosfatos (Uranilo) group. This specimen comes from Mina Assunção, Aldeia Nova, Ferreira de Aves, Viseu, Portugal.

Furcalita Laminar from Mina Assunção, Aldeia Nova, Ferreira de Aves, Viseu, Portugal — Terrium

Description

Undamaged phurcalite plates, well crystallized in stacked groups of an intense lemon-yellow colour, growing over a carpet of primary meta-autunite. The fluorescence of the whole specimen under UV light is absolutely stunning.

History of this specimen

These specimens were collected by Antonino Bueno and Carlos González Bargueño during their 2015 trip to Assunção. After spending quite some time digging through areas thought to be played out, they came across some very promising damp cavities. They worked the spot with as much excitement as care and ended up opening an incredible pocket of uranium minerals: sharply crystallized specimens with intensely vivid colours, very well preserved in the damp environment inside the cavity. That find yielded a few real gems, three of which I keep in my collection: this phurcalite, an autunite, and a primary meta-autunite.

About Furcalita

First described in 1978 by Michel Deliens and Paul Piret, phurcalite gets its name as an acronym of its composition: PHosphate, URanyl, and CALcium. It shares the same chemical building blocks with autunite (calcium, uranium, phosphorus, oxygen, and hydrogen). Both are hydrated calcium uranyl phosphates, but their proportions and crystal structures differ. Although it is commonly seen as acicular crystals, elongated prisms, or radiating sprays, the abstract of the original 1978 description opened with «La phurcalite se présente en plaquettes jaunes» — yellow platelets which, as in this specimen, can closely resemble autunite.

About the locality

Assunção is a pegmatite deposit hosted by the Ferreira de Aves granite, worked as an open pit for quartz and feldspar. As well as large beryl crystals, it has yielded uranium phosphates such as autunite and torbernite. The former pit was altered by later enlargement and is partially flooded. The property is private and access is restricted: permission is required to enter or collect, and an alarm system is in place.

Technical data

Catalogue No.
0667
Composition
Ca₂(UO₂)₃O₂(PO₄)₂·7H₂O
Name
Furcalita
Variety
Laminar
Group
Fosfatos (Uranilo)
Category
Núcleus Ardens
Matrix
cuarzo
Associations
meta-autunita primaria
Mine
Mina Assunção
District / Municipality
Aldeia Nova
Province
Ferreira de Aves
Region
Viseu
Country
Portugal
Size (cm)
6.5 x 4.3 x 2
Weight
53.2 g
Ex-collection
Antonino Bueno Yanes
Quality
Top
Value trend
Al alza

Related specimens

← Back to Terrium catalogue