Gas hydrates are primarily found in unconsolidated sands (upper row) or clays (center row). Hydrates also commonly occur in thin, hydrate-bearing sand layers separated by fine-grained sediment (upper right), and can even form in sands that have themselves been consolidated, or packed more tightly together, to form a rock (lower right). In clays, gas hydrates can exist in low concentrations in the small pores between grains (center left). Gas hydrates in higher concentrations tend to displace grains to form veins, lenses, and nodules (center right), and those veins, lenses or nodules can occasionally grow large enough to appear as a massive hydrate occurrences (lower left).
From collection: Frozen Heat - A Global Outlook on Methane Gas Hydrates