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The Mineral strengite

Purple Strengite Balls

Strengite is the end member of a series with Variscite, with Strengite being the iron-dominant member and Variscite being the aluminum-dominant member. Though similar in composition, Strengite and Variscite strongly differ in their color. While Variscite has greenish hues, Strengite is mostly in violet or reddish. The color caused by iron will dominate, and will cause Variscite rich in iron to have a violet or reddish color similar to Strengite.

Strengite is named in honor of Johann August Streng (1830-1897), a Professor of Mineralogy at the University of Giessen in Germany.

Chemical Formula

FePO₄ · 2(H₂O)

Color

Purple, pink, reddish-pink, red. Rarely white to yellow.

Crystal System

Orthorhombic

Properties

Streak
White

Hardness
3.5 - 4

Transparency
Transparent to translucent

Specific Gravity
2.6 - 2.8

Luster
Vitreous, pearly

Cleavage
1,1;2,1

Fracture
Splintery, uneven

Tenacity
Brittle

Crystal Habits

Most often as rounded balls of tiny radiating crystals. Also in botryoidal crusts, reniform, rosettes, and massive. Individual crystals and microcrystals are usually prismatic, bladed or tabular, and often with pointed or angled terminations.

3D Crystal Atlas

Additional Information

Composition
Iron phosphate, often with some aluminum

In Group
Phosphates; True Phosphates

Striking Features
Color and crystal habits.

Environment
As a secondary mineral in phosphate pegmatite deposits, and in iron-rich sedimentary sandstones.

Uses

Strengite is a rare collectors mineral. It doesn't form in large crystals, but small crystal aggregates and crystals make beautiful thumbnail and micromount specimens.

Noteworthy Localities

Some of the largest single Strengite crystals were found in Pleystein, Bavaria, Germany. This locality is closed, and these specimens have become classics that are very difficult to obtain. Good Strengite crystals were also found nearby in Hagendorf, the next town over from Pleystein. Outstanding and highly aesthetic hemispherical Strengite balls with a deep violet color come from the Leveäniemi Mine, Svappavaara, Sweden. Portugal has several Strengite localities, most notable is the the Cabeço da Mua mine, Felgar, where it occurs as small pink crystals. In Brazil, small pink and purple balls come from the Boa Vista pegmatite, Conselheiro Pena, in the Doce valley, Minas Gerais.

In the U.S., velvety purple Strengite aggregates come from the phosphate deposit at Indian Mountain, Cherokee Co., Alabama. Other localities include the Three Oaks Gap, Polk Co., Arkansas; the Bull Moose Mine, Custer, South Dakota; and the Stewart Mine, Pala, San Diego Co., California.