TERRIUM — A mineralogy cabinet

Yeso

Yeso is a mineral with formula CaSO₄·2H₂O, in the Sulfatos group. This specimen comes from Mina San Timoteo-Humboldt, La Unión, Cartagena, Región de Murcia, España and joined the Terrium collection in 2006.

Yeso from Mina San Timoteo-Humboldt, La Unión, Cartagena, Región de Murcia, España — Terrium

Description

Colourless prismatic crystals to 1 cm, arranged in fan-like sprays on dark grey earthy matrix. Complete transparency and excellent lustre, with a clean, sculptural aesthetic uncommon in gypsum.

History of this specimen

This specimen is on Mindat, minID: XUW-HJJ. Bought in 2025 from Marcos, who offered it to me from his personal collection. It is ex collection Alfonso Rodríguez Ruiz. Its sculptural character and the purity of its crystals make it an uncommon gypsum, and there is also a somewhat complicated story behind it. The original collector labelled it as from the Brunita opencast quarry, but that is an error; it actually comes from the San Timoteo-Humboldt mine, something that became known later. Jordi Fabre relates, second-hand, that those who found these gypsum specimens and their companions set about sowing confusion: first they said they came from El Gorguel, later they said nothing; afterwards they burnt tyres so that the smoke would spoil the gypsum that remained and thus inflate the price.

About Yeso

Typical San Timoteo habit. Monoclinic polymorph of hydrated calcium sulphate; in stable underground environments it develops very pure prismatic fans, immediately recognisable within this deposit.

About the locality

These gypsum specimens, erroneously attributed for years to the Brunita quarry, actually come from a hypogene microenvironment within the interlinked galleries of the San Timoteo and Humboldt mines at Portman (Sierra Minera de Cartagena-La Unión). The confusion with Brunita probably arose from the Humboldt concession no. 3179 (holder Ángel Bruna, 1949), but the surface conditions of the quarry rule out that origin. Their singularity is due to an exceptional subterranean environment: slow flow of mineralised waters, mixing with reducing gases, and prolonged thermal stability—factors that allowed the formation of colourless, transparent prismatic fans of exceptional purity. The deposit suffered an incomprehensible but deliberate act. A tyre was burnt inside the galleries to prevent anyone ever again from extracting such pure gypsum from there. What has continued to come out is obviously stained by the soot.

Technical data

Catalogue No.
0088
Composition
CaSO₄·2H₂O
Name
Yeso
Group
Sulfatos
Category
Cresta Montis
Matrix
Matriz terrosa gris oscura
Mine
Mina San Timoteo-Humboldt
District / Municipality
La Unión
Province
Cartagena
Region
Región de Murcia
Country
España
Size (cm)
5 x 4.5 x 3.5
Weight
52.2 g
Acquired
2006
Ex-collection
Alfonso Rodríguez Ruiz > Marcos López (Ponferrada)
Etymology
From the Greek "gypsos", meaning "plaster" or "chalk". Its use is ancient: from Egyptian construction to classical art.
Quality
Top
Value trend
Al alza

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