OK – I’m taking huge liberties with this blog challenge. My take on “mustard” is this honey-mustard or Grey Poupon mustard-coloured calcite specimen. It is an example of a speleothem – or cave calcite. The layered portions are similar to onyx and the bubbly, blobby bits are popcorn calcite. We found this in a tufa outcrop along a river near our home. The spring runoff of 2008 eroded away a great mass of the tufa. Exposed were several cavities at the interface of a calcite-cemented conglomerate unit and the tufa unit. The pieces we found were broken off and lying in the rubble at the base of the damaged tufa outcrop.
Inspired by Jennifer Nichole Wells’ One Word Photo Challenge