1. 
   Greywacke
   Greywacke or Graywacke (German grauwacke, signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a tex...
   Found op http://en.wikipedia.org/wiki/Greywacke
   
   
2. 
   Greywacke
   A dark-coloured rock common in the Southern Uplands, and used extensively in church buildings there. It cannot be dressed to a fine finish.
   Found op http://www.maintainyourchurch.org.uk/ToolkitModules/Toolkit1Glossary/tabid/
   
   
3. 
   greywacke
   (German: grauwacken; grau grey; ) is a hard and durable grey rock with no structure (like layers). It was re-formed (metamorphosed) from sedimentary rock (with layers) under pressure and heat, between 65 and 270 million years ago. It forms the foundation of many ranges and shores of NZ. It is now al...
   Found op http://www.seafriends.org.nz/books/glossary.htm
   
   

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