At Erongo, siderite is pretty much just an accessory mineral.  You see it third-wheeling pretty combinations of aquamarine and schorl, or lurking annoyingly off to the side on a matrix who's focus is something else.  But this piece is actually a good siderite in its own right.  The crystal is particularly large and sits nice and centered, surrounded by dirty crystals of what is probably the only other (common) mineral found on erongo that it can eclipse: feldspar. I see at least one twinned feldspar though...