Ludlamite

Chemical formula: Fe<sup>2+</sup><sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·4H<sub>2</sub>O

A hydrated iron phosphate valued for its intensely green, wedge-shaped crystals and attractive vitreous luster.

## Characteristics Ludlamite is a hydrated iron phosphate that forms distinctive, well-developed crystals. They most commonly adopt tabular, wedge-shaped, or short prismatic forms. They usually occur as small, overgrown groups and druses in rock cavities. A distinguishing feature of ludlamite is its vivid, apple-green color, which, combined with its vitreous luster and high transparency, makes it an attractive mineral for collectors. Crystals rarely exceed 2-3 cm, although exceptional, larger specimens are known. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3.5, making it susceptible to scratching. It has a vitreous luster, and on cleavage planes, it can be pearly. It is transparent to translucent. Its density ranges from 3.12 to 3.19 g/cm³, making it noticeably heavier than typical rock-forming minerals like quartz. ## Colors and Varieties Ludlamite is almost exclusively green. The color palette ranges from light green, through intense apple-green, to emerald green. On the surface, it can weather and oxidize into brownish or reddish iron oxides, which form coatings on it. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1877 by the English chemist Frederick Field, commemorates Henry Ludlam (1824-1880), a British mineral collector, in whose collection this new species was first identified. The type specimen was material from the Wheal Jane tin mine in Cornwall, England. ## Uses Ludlamite has no industrial application. It is exclusively a valued and sought-after collector's stone.

Properties

Mohs hardness
3.5
Luster
Vitreous
Streak
Pale greenish-white
Density
3.12-3.19
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The most important diagnostic feature of ludlamite is its characteristic apple-green color combined with wedge-shaped or tabular crystal forms. Perfect cleavage in one direction, vitreous luster, and relatively low hardness (3.5) are also key. Occurrence in paragenesis with other phosphates (such as vivianite or triphylite) in pegmatites or hydrothermal veins is a strong indicator. ## Distinguishing from Similar Minerals Ludlamite is sometimes confused with vivianite, which, however, usually has a blue, dark green, or almost black color, and its crystals are prismatic or bladed. Annabergite (nickel bloom) has a similar green color but most often forms coatings and acicular aggregates in the oxidation zones of nickel deposits. Other green phosphates, like phosphosiderite, have a different color (lavender) and crystal form. ## Crystal Forms Ludlamite crystals are monoclinic, most often thick tabular, wedge-shaped, or short prismatic. They often form fan-like or radial aggregates. They also occur as druses covering rock fissures or other minerals.

Geological environment

## Genesis Ludlamite is a secondary phosphate mineral. It forms in the oxidation zones of complex granitic pegmatites or in some hydrothermal ore veins. It forms as a result of the alteration and weathering of earlier, primary phosphate minerals, mainly triphylite and its varieties. ## Mineral Associations This mineral often co-occurs with other phosphates and sulfides. Its typical associated minerals include: siderite, triphylite, vivianite, phosphoferrite, pyrite, chalcopyrite, sphalerite, and quartz. ## Localities The world's most famous ludlamite specimens, valued for their size and crystal quality, come from the Blackbird Mine in Lemhi County, Idaho (USA). Excellent crystals have also been found in Bolivian tin mines, e.g., Siglo XX and Huanuni. Other important localities include the Hagendorf-Süd pegmatite in Bavaria (Germany), the Santa Eulalia mine in Chihuahua (Mexico), and the historical locality in Cornwall (United Kingdom).

Rarity

Rare

For collectors

## Quality Criteria The most highly valued ludlamite specimens are characterized by an intense, saturated green color, high transparency, and sharply defined, undamaged crystals. The size of the crystals is of great importance – those exceeding 1 cm are already considered valuable. Aesthetically pleasing compositions are particularly sought after, in which green ludlamite crystals contrast with a light rock matrix or other minerals, such as brown siderite. ## Popular Localities The localities in Idaho (USA) and Bolivia (especially from the Siglo XX mine in Llallagua) are considered classic and provide the best specimens. Specimens from these localities command the highest prices and are the pride of advanced systematic and regional collections.

Care and storage

## Cleaning Ludlamite specimens should be cleaned very carefully due to their softness and perfect cleavage. It is best to use a soft brush to remove dust. If necessary, the specimen can be rinsed in distilled water and then thoroughly dried. Absolutely avoid ultrasonic cleaners, which can cause it to disintegrate. ## What to Avoid The mineral is sensitive to impact and pressure. It should be protected from contact with acids and other strong chemicals. Prolonged exposure to direct sunlight, which can cause discoloration, is not recommended. High temperatures should also be avoided. ## Storage It is best to store ludlamite in separate, padded boxes to prevent scratches and mechanical damage. Specimens on a rock matrix should be displayed stably, in closed display cases that protect against dust and sudden changes in humidity.

External references

Sources

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