by Squirrel Girl » Dec 15, 2015 7:15 am
Sorry I missed this post earlier.
Identifying rocks by pictures is often difficult. So I don't guarantee my answers, but here's what I interpret.
Both the rocks appear to be limestone. The whiter rock is what geologists would call "friable." That means it crumbles easily. There are several ways that come to mind how it might have formed. One is that it is "chalk." That is a type of limestone that forms by microscopic organisms that have tiny calcite shells. The organisms live up in the water column, but when they die, they sink to the sea floor. The soft tissue decomposes, but the tiny shells build up. The White Cliffs of Dover in the UK formed that way.
Alternatively, the white material might contain some clay that contaminates the limestone. Marl is a clay-rich limestone and it tends to be friable.
Finally, there could have been some recent weathering that weakened the rock.
The "red" material is typical-looking limestone. It is rather massive and quite hard. The buff color might come from dust or iron oxides that were deposited at the same time as the calcite. Another possibility is that it is dolomite instead of limestone. Dolomite is very similar, but it has some magnesium substituted into the calcite structure in place of calcium.
I hope this helps.
Barbara Anne am Ende
"Weird people are my people."