Siderite is a very common mineral, in lustrous or iridescent deep brown forms, rarely in paler brown translucent balls. Generally it is in sheaf-like bundles, occasionally in ‘bow-ties’. It does occur in rhombs, often with curved multiple surfaces, and these are frequently hollow, with maybe a chabazite or two inside. Possibly the rhombs were originally calcite, coated with siderite, and the calcite has etched out.
Orthoclase occurs as translucent white bladed crystals lining many of the cavities, rarely large or well formed.
Below: Siderite with orthoclase, Bickers Quarry (Simpkins Quarry), Tokatoka, Kaipara District, Northland Region, North Island, New Zealand. Width of view 6mm.
