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Phosphosiderite Properties, Facts and Photos

phosphosiderite mineral sphere

What is Phosphosiderite?

Phosphosiderite is a relatively rare mineral first discovered in 1858.  It was named in 1890 after its main constituents which are phosphate and iron.

The name phosphosiderite comes from 'phospho' (from phosphate) and 'siderite' from the Latin 'sídēros' meaning 'iron'.

This naturally occurring form of iron phosphate can only be found in a handful of locations worldwide.  Most phosphosiderite comes from Germany, USA, Portugal, Chile and Argentina.

Although once known as metastrengite this name is now mostly obsolete.

Crystals of phosphosiderite occur in shades of red and pink and tend to be extremely small.  This mineral occurs more widely with a massive or botryoidal crystal habit.  This material is mainly used for lapidary purposes.

In mineralogy the term crystal habit describes the external shape of a crystal or group of crystals and how well it/they have formed.  The habit described as massive means the mineral's crystals grow tightly together as one large mass.  Unlike individual well-formed crystals they have no visible internal structure and no distinguishable external shape.

An good example of a mineral whose crystals occur in this way is turquoise. the mineral turquoise embedded in rock matrix

The crystal habit described as botryoidal means crystals have a rounded shape.  The word comes from the ancient Greek word 'botrys' meaning 'bunch of grapes'. malachite with a botryoidal crystal habit

Phosphosiderite that occurs in massive form can be found in striking shades of lilac, lavender and purple.

Phosphosiderite can feature yellow spidery veins which are inclusions of cacoxenite (ka~cox~enite).  This iron aluminium phosphate mineral usually but not always occurs within other minerals.

Phosphosiderite is believed to have started off as the abundant phosphate mineral triphylite. Over long periods of time and through various geological processes triphylite turns into phosphosiderite.

Phosphosiderite is typically found in a type of igneous rock called a pegmatite.  Pegmatites form when magma crystallises.  The rocks often contain unusually large crystals.

Minerals that are rarely found in other types of rock are often present in pegmatites.

Geologists believe phosphosiderite may be present in soils.  The process would begin when rocks containing phosphosiderite break down.

It's also believed phosphosiderite may replace bone and shell.  This can happen under certain geological conditions when the natural minerals in these materials are replaced with phosphosiderite.  This preserves the shape and structure of the original organic material. 

This geological process is similar to what happens with petrified wood.
phosphosiderite tumbled stones
On Mohs scale of mineral hardness phosphosiderite grades 3.5 to 4 so must be handled carefully.  It's also very brittle and will break easily.

Article Pictures

The picture of the mineral turquoise in rock matrix is courtesy of Stan Celestian.

The malachite with a botryoidal crystal habit is courtesy of Ron Wolf.

The phosphosiderite tumbled stones are from our collection.

Pictures are clickable and redirect to the original image.

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