TERRIUM — A mineralogy cabinet

Boltwoodita

Boltwoodita is a mineral with formula K(UO₂)(SiO₃OH) · H₂O, in the Silicatos group. This specimen comes from Green Monster Mine, Goodsprings District, Clark County, Nevada, Estados Unidos and joined the Terrium collection in 2025.

Boltwoodita from Green Monster Mine, Goodsprings District, Clark County, Nevada, Estados Unidos — Terrium

Description

Abundant yellow boltwoodite aggregates standing out on the matrix. The crystal-covered area measures c. 3 x 2 centimetres. Excellent under the hand lens.

About Boltwoodita

A hydrated potassium uranyl silicate that characteristically crystallises as yellow hedgehog-like aggregates. It is a secondary mineral: rainwater percolated through fractures, dissolved uranium and, reacting with potassium and silica in the Nevada rocks, precipitated these yellow boltwoodite crystals, sometimes visible to the naked eye; in this specimen, best appreciated with a hand lens.

About the locality

This Nevada mine, opened in 1894 for zinc and lead, later became a world reference for the boltwoodite crystals formed in its uranium zones. After its final closure in 2013 to protect local fauna (principally the desert tortoise and bat colonies) and to secure the tunnels, no new material can be collected, making existing pieces limited and of increasing historical interest.

Technical data

Catalogue No.
0401
Composition
K(UO₂)(SiO₃OH) · H₂O
Name
Boltwoodita
Group
Silicatos
Category
Núcleus Ardens
Matrix
Dolomita
Mine
Green Monster Mine
District / Municipality
Goodsprings District
Province
Clark County
Region
Nevada
Country
Estados Unidos
Size (cm)
4.1 x 3.1 x 1
Acquired
2025
Etymology
Named after Bertram Boltwood (1870–1927), an American chemist who transformed geology by demonstrating that uranium decays to lead. In 1907 he proposed using that relationship to calculate the age of rocks, initiating the method that first allowed geologists to determine the Earth's age in millions of years.

Related specimens

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