Conglomerates are sedimentary rocks comprised of pebble to boulder sized clasts (fragments) of other rocks, held together by a fine grained matrix (background material). Conglomerates are similar to Breccia, but the roundness of the clasts differentiates the two. Conglomerates form in high-energy environments, like rivers and beaches, where the transport of the clasts gradually smooths their edges and rounds them.  The clasts within a conglomerate can look very different, in texture and colour, as they might not be the same rock type! Any rock that falls into the water upstream or along the ocean coastlines can be rounded and added to the conglomerate.

The finer grained matrix then cements the clasts together, forming a rock. The matrix of a conglomerate can vary but is usually fine sand, with some calcite or clay present.

Conglomerates can be sorted into types by a variety of characteristics, such what type of rock the clasts are, how many types of clasts there are, and how big the clasts are.

Rocks supplied by:

Lucy and Grant Middendorf 
E: info@wanakastone.co.nz