Mitridatite

Chemical formula: Ca₂Fe³⁺₃O₂(PO₄)₃(H₂O)₂·H₂O

Mitridatite is a rare phosphate mineral, forming characteristic, dull, earthy coatings and crusts in shades from green to brown.

## Characteristics Mitridatite is a hydrated calcium iron phosphate belonging to the mitridatite group. It most commonly occurs as very fine-grained, earthy or dull coatings, crusts, and masses filling rock fractures. It rarely forms rosetted or spherical aggregates composed of microscopic, tabular crystals. Due to its structure, individual crystals are usually unrecognizable to the naked eye, and specimens appear as compact, porous, or powdery aggregates. ## Physical Properties Mitridatite crystals are very soft, with a Mohs hardness of about 2.5, meaning they can be scratched with a fingernail. The mineral is relatively light. The luster is typically dull or earthy, sometimes waxy in more compact aggregates. It is opaque or at most translucent on thin edges. ## Colors and Varieties Mitridatite exhibits a wide range of colors, most commonly in shades of green: from olive-green, through greenish-brown, to yellowish-green. Brown, reddish-brown, and yellow specimens also occur. The color variation is mainly due to the oxidation state of iron in the mineral's structure. No named varieties are distinguished. ## History and Name The mineral was first described in 1914 by P. A. Dvoychenko. Its name comes from Mount Mithridat on the Kerch Peninsula in Crimea (Ukraine), which is its type locality. The mountain's name, in turn, honors Mithridates VI Eupator, King of Pontus, who, according to legend, was interested in poisons and antidotes, and the region contains iron deposits from whose oxidation this mineral forms. ## Uses Mitridatite has no industrial significance. However, it is valued by collectors specializing in rare phosphate minerals and minerals from specific localities (so-called "locality collecting").

Properties

Mohs hardness
2.5
Color
Greenish-yellow, olive green, brownish-green, etc.
Luster
Earthy, Resinous
Streak
pale green
Density
0
Cleavage
{100} observed on crystals from Gap Lode Pegmatite, South Dakota
Fracture
Irregular/Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Mitridatite is identified by its characteristic appearance: dull, earthy, or waxy coatings and crusts in shades of green and brown. Key features include low hardness (about 2.5) and its occurrence as an oxidation product of other phosphate minerals in pegmatites or sedimentary rocks. ## Distinguishing from Similar Minerals It can be confused with other secondary phosphate minerals of similar colors, such as rockbridgeite, dufrenite, or cacoxenite. Differentiation often requires advanced analytical methods (e.g., XRD). In the form of green coatings, it is also sometimes confused with some copper minerals, but mitridatite is associated with iron phosphates, not copper sulfides. ## Crystal Forms Well-formed crystals are extremely rare and appear as microscopic, thin tabular crystals. It usually forms spherulitic or rosetted aggregates, and most often occurs as compact, earthy masses, crusts, and coatings.

Geological environment

## Genesis Mitridatite is a secondary mineral. It forms mainly as a result of hydrothermal alteration or weathering of primary phosphate minerals, especially those containing iron, such as triphylite and lithiophilite, in the oxidation zones of granitic pegmatites. It can also form in oolitic sediments rich in iron and phosphorus. ## Mineral Associations It often co-occurs with minerals from which it forms or which it accompanies during weathering. Typical associated minerals include rockbridgeite, strengite, hureaulite, vivianite, cirrolite, wardite, eosphorite, as well as iron oxides (goethite, limonite) and quartz. ## Localities Important worldwide localities that yield well-formed specimens include the Palermo and Fletcher mines in North Groton, New Hampshire (USA); the Tip Top mine in South Dakota (USA); and the Bull Moose Mine, also in South Dakota. It also occurs on the Kerch Peninsula in Ukraine (type locality), in Mangualde, Portugal, and in the Hagendorf area in Bavaria (Germany).

Rarity

Not very common

For collectors

## Quality Criteria Most valued by collectors are specimens where mitridatite forms distinct, spherulitic or rosetted aggregates of intense olive-green color. Rich coatings on contrasting rock matrix are also highly prized. Specimens with well-defined crystals, though microscopic, are exceptionally rare and sought after. Association with other rare phosphate minerals is also important. ## Popular Localities American localities are considered classic and provide the best quality specimens, especially the Tip Top and Bull Moose mines in South Dakota and the Palermo mine in New Hampshire. Specimens from these locations are characterized by well-formed aggregates and intense color.

Care and storage

## Cleaning Mitridatite specimens are very delicate and porous. They should only be dry-cleaned, using a soft brush to remove dust. Due to its softness and often earthy form, washing with water is discouraged – it can lead to the disintegration or damage of the specimen. ## What to Avoid Contact with water, acids, and other chemicals should be strictly avoided. The mineral is sensitive to shocks and abrasions due to its low hardness. It should not be heated or exposed to sudden temperature changes. ## Storage Mitridatite specimens are best stored in closed, padded collector boxes to protect them from dust, mechanical damage, and moisture. Due to its fragility, it is not suitable for display in open showcases without adequate protection.

External references

Sources

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