The grains are not only large, but also round - this rock is formed by pebbles, which have previously been rounded by water. They are marine rocks, formed under water.
Fossils are seldom present due to the conditions in which they are formed. They are formed when water carries sediments in a flow.
The heaviest parts are deposited first and become conglomerate. Other particles are carried further and become other, finer grained rocks.
In normal, long-term water flow the sediments are sorted in that way before they are deposited.
Sometimes, though, if rapid deposition happens in short-term flows, the sediments are not sorted that well and the grain size of conglomerate can be mixed.
What minerals are present? Any! This is a term, just like breccia or pegmatite, which applies to a rock's texture and not chemical composition.
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