Imagine we have a sedimentary rock – dolomite I think (Calcuim/Magnesium carbonate). Then we get some magma welling up from inside the earth – an igneous intrusion – this is the granite.
Water circulates though the system through the magma, coming up through the cooling granite and out into the dolomite.
Through the magma it leaches minerals (perhaps molybdenite if we’re lucky) and the hot fluid coming into the dolomite changes the crystal structure to a mineralised marble. This hydrothermally metamorphosed region being called a skarn.
Presumably this wasn’t happening a little all over the place since the mineralisation isn’t significantly disseminated. But it was largely flowing through bigger fractures so we have large mineralised chunks – massive mineralisation.
Now molybdenite is a hexagonal crystal whose planes slip over each over very easily. Like graphite and a very good lubricant.
If it was disseminated, it’s physical properties wouldn’t matter much as you’ve only got a little in the midst of the rock. But as it’s massive they do matter and so “laminated, flaky & friable” are plausible words.
To any geologists out there – sound a fair description from an amateur?
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