Minerals from the Muschelkalk quarry of Winterswijk, The Netherlands
Henk Oosterink (The Netherlands)
In the past, I have written about fossils from the Muschelkalk of Winterswijk (the Netherlands) (see Diversity of trace fossils from the Anisian (Middle Triassic) of Winterswijk, The Netherlands, Invertebrate fossils from the Lower Muschelkalk (Triassic) of Winterswijk, The Netherlands and Triassic reptiles from the Lower Muschelkalk of Winterswijk). In this article, I will cover the minerals at this quarry, where eight different minerals can be found. The quantities are too small for commercial exploitation, with only the limestone of concern to the company that works the quarry (Ankerpoort). Despite this, mineral-collectors frequently pay special visits to this site.
Pyrite (FeS2) = iron sulphide. Crystal system = cubic. Etymology: the name is derived from “pyr”, which means fire in Greek.
The best-known mineral from the quarry is undoubtedly pyrite.
In this region, pyrite is also called “Winterswijk gold”. It can be found in a number of crystalline forms, but most forms are cubic (Fig. 2).
Other forms are octahedral and pentagonal dodecahedral (Fig. 3). In some solid layers of rock, pyrite can also be found in nodular form, which is largely made up of very small, cubic crystals formed from a kernel in an outward direction (Fig. 4).
Pyrite can sometimes display a rainbow of colours, including greens, reds, oranges and violets (Fig. 5). These are caused by the presence of small crystals, especially when in combination with calcite.
Marcasite (FeS2) = iron sulphide. Crystal system = rhombic. Etymology: from the Assyrian name for a province in north-eastern Iran (Persia) “Markhashitu”.
Marcasite has the same chemical composition as pyrite, but with a different crystalline structure and colour (Fig. 6). The latter is mainly copper-yellow or yellowish green, but, when oxidised, it is darker. At Winterswijk, marcasite occurs with white calcite in little cavities in the limestone.
Calcite (CaCO3) = calcium carbonate. Crystal system = trigonal. Etymology: calcite is derived from “calx”, meaning pebble in Latin.
Calcite in Winterswijk is mostly milky-white, rather than transparent. For the greater part, the limestone in the quarry is made up of calcareous material, together with calcite. In certain levels of the limestone, there are little cavities. The sides of these are lined with pointed calcite crystals (nests with so-called calcite-scalenoeders; Fig. 7). Calcite is frequently found together with celestine.
Galena (PbS) = lead sulphide. Crystal system = cubic. Etymology: from the Latin, simply meaning lead ore.
Galena crystals are found in a thin layer, about 6cm thick, which is very hard – the galena layer (Fig. 8). It is the most important plumb ore in the world, as it contains lead. When you break this layer, silver-coloured crystals of galena are visible, but these are also likely to be broken. When oxidised, the silver-coloured glitter changes into dull-grey crystals. Sometimes, there are tiny cubic or octahedral crystals present in little cavities in the limestone.
Sphalerite (ZnS) = zinc sulphide. Crystal system = cubic. Etymology: the name is derived from the Greek “sphaleros”, meaning treacherous, as sphalerite has been mistaken for galena.
Sphalerite is the most important zinc ore (Fig. 9). It is very rare in the Winterswijk quarry. It occurs as little glossy, dark-brown crystals.
Celestine (SrSO4) = strontium sulphate. Crystal system = rhombic. Etymology: from the Latin word “caelum”, which means the sky.
Celestine in Winterswijk has different colours that range from colourless to white, blue, yellow or red. The mineral is slightly transparent. In general, celestine has a blue colour (Fig. 10), but most Winterswijk celestine has been stained red from the layers above (Fig. 11).
It is mostly deposited in nodules (geodes) at certain levels lower in the quarry. When there are cavities in these nodules, the celestine mostly appears as fine crystals. However, most of the time, it appears as cleft filling, with a thickness of some millimetres in almost horizontal layers of limestone. The mineral is also present as a fibrous structure.
Strontianite (SrCO3) = strontium carbonate. Crystal system = rhombic. Etymology: from the Scottish mining village, Strontian, in western Lochaber.
Strontianite was found in Winterswijk for the first time in 1992. It consists of a very small, white aggregate of transparent needles on celestine crystals (Fig. 15).
Gypsum (CaSO4.2H2O) = calcium sulphate. Crystal system = monoclinic. Etymology: from the Greek, meaning chalk, plaster or cement.
Gypsum appears as very small crystals, which can only be found in dry areas of the quarry, together with oxidized pyrite. The crystals are mostly found as transparent needles and are colourless. This mineral is found throughout the world and is generally the result of the evaporation of warm seawater.
Acknowledgements
My thanks to Bernhard Smit (Winterswijk) for help with this article. Most of the pictures come from my own collection.
References
Oosterink, H.W. (1986) – Winterswijk, geologie deel II. De Trias-periode (geologie, mineralen en fossielen). Wet.Mededelingen KNNV 178: 1 – 120.
Oosterink, H.W. & H. Winkelhorst (2003) – Vondstmelding van gips. Grondboor & Hamer 6: 116 – 117.
Peletier, W. & H.W. Oosterink (1994) – Een nieuw mineraal uit de Winterswijkse steengroeven. Grondboor & Hamer 4/5: 85 – 86.
Peletier, W. & H.W. Oosterink (1995) – Een vindplaats van mineralen in Nederland: de Winterswijkse steengroeve. Grondboor & Hamer 1: 1 – 5.