What Exactly is Phosphosiderite?
Phosphosiderite is a relatively rare mineral first discovered in 1858 and 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 small number of locations worldwide some of which include Germany, USA, Portugal, Chile and Argentina. Although once known as metastrengite this name is now virtually obsolete.
Crystals of the mineral phosphosiderite occur in shades of red and pink and tend to be extremely small. It occurs more widely with a massive or botryoidal crystal habit and this material is mainly used for decorative purposes. In mineralogy crystal habit describes the external shape of a crystal or group of crystals and how well it or they have formed. The crystal habit described as massive means the mineral has masses of crystals with no visible internal structure and no distinguishable external shape.
An example of a mineral whose crystals occur in this way is turquoise. Crystal habit described as botryoidal means the crystals have a rounded shape. The word comes the Ancient Greek word 'botrys' meaning 'bunch of grapes'.
Turquoise mineral embedded in rock matrix
Malachite with botryoidal crystal habit
The phosphosiderite that occurs in massive form can be found in striking shades of lilac, lavender and purple. Most of this material is transformed into cabochons for use in jewellery. This type of phosphosiderite can feature yellow spidery veins which are inclusions of cacoxenite (pronounced ka~cox~enite). This iron aluminium phosphate mineral usually but not always occurs within other minerals.
On Mohs scale of mineral hardness phosphosiderite grades 3½ to 4 which is fairly soft. It's also brittle so must be handled carefully.
The photos of the minerals turquoise and malachite in our article are clickable and redirect to the original full size image. Photos courtesy of Stan Celestian (turquoise) and Ron Wolf (malachite).
https://www.mindat.org/photo-980160.html (phosphosiderite photo on Mindat)
Cacoxenite Microscopic Images; https://www.topminerals.info/index.php?searchterms=cacoxenite&searchauthor=-&level=search&author=-