Rillenkarren – Erosion of rock during Oman’s wetter phase.
The technical description from my geology book says:
Rillenkarren.- Are forms of dissolution on the surface of the rocks that consist of small channels separated by sharp crests configuring a network of tight more or less parallel gullies next to each other. Its Genesis is linked to the dissolution of the rock by the sheet of water that forms on it as a local run-off.
David A Lockwood 
Lovely stone! This IS a stone? I.e. Small-ish? And fascinating
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Sort of, about 20″ x 15″ x 10″ or there about.