TERRIUM — A mineralogy cabinet

Siderita

Siderita is a mineral with formula FeCO₃, in the Carbonatos group. This specimen comes from Minas da Panasqueira, Aldeia de S. Francisco, Covilhã, Castelo Branco, Portugal and joined the Terrium collection in 2025.

Siderita from Minas da Panasqueira, Aldeia de S. Francisco, Covilhã, Castelo Branco, Portugal — Terrium

Description

Brown siderite crystals completely coat a massive milky quartz crystal. The outer surface shows scaly aggregates, with possible scattered green fibres, which appear to be fresh, unoxidised siderite scales or minor inclusions.

About Siderita

A typical iron carbonate of hydrothermal veins, siderite is frequently associated with quartz, sulphides and fluorite. At Panasqueira it is part of the classic suite of gangue minerals that accompany tungsten mineralisation, with habits ranging from well-formed rhombohedral crystals to laminar aggregates, crusts and more massive coatings. Its brown, ochre or golden colour is often intensified by surface alteration of iron.

About the locality

Panasqueira is one of the most important European deposits for hydrothermal tungsten minerals and a classic Portuguese collecting locality. Its quartz veins have produced highly recognisable associations with wolframite, arsenopyrite, siderite, apatite, fluorite, micas and sulphides. In small specimens like this, the piece retains the typical look of the deposit: quartz as support, dominant ferruginous siderite and scattered accessory minerals.

Technical data

Catalogue No.
0554
Internal reference
X0137
Composition
FeCO₃
Name
Siderita
Group
Carbonatos
Matrix
Cuarzo
Associations
Fluorita
Mine
Minas da Panasqueira
District / Municipality
Aldeia de S. Francisco
Province
Covilhã
Region
Castelo Branco
Country
Portugal
Size (cm)
5 x 3 x 2.5
Acquired
2025
Etymology
From the Greek 'sideros' ('iron').
Quality
Buena
Value trend
Estable

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