Phosphosiderite is a distinctive mineral that's a form of iron phosphate. Most of the world's supply comes from Chile.
Although used for decorative purposes phosphosiderite is not used that often in jewellery. This is likely to be because it's relatively soft and brittle. This characteristic makes cutting and polishing difficult.
This colourful cabochon has been mounted in a handmade sterling silver setting.
This phosphosiderite pendant has been slightly reduced because of a minor firescale mark. It can just about be seen in our second photo.
Firescale resembles a tea stain. It can appear when some metals are heated at very high temperatures. It's caused by an interaction between the silver and oxygen and is more difficult to avoid in hand-crafted jewellery.
When the silver is well polished the firescale mark is almost unnoticeable. As it begins to tarnish it can become more visible.