Design/Aesthetic Sets: In architecture and interior design, a "slate and limestone series" often refers to a product line of flooring or wall tiles that offers both materials as complementary options to create contrast (e.g., a dark, rustic slate paired with light, neutral limestone).

Geological Sequences: In some regional geological surveys, you may find stratigraphic "series" or sequences where layers of sedimentary limestone are found deposited in close proximity to, or even interbedded with, metamorphosed shales (slates). These are distinct layers, not a single type of rock.

Gaming Mechanics: In simulation games like RimWorld, stone types are often categorized into a list or "series" of available building materials. Players often compare the two based on their aesthetic (color) or utility (durability/mining speed).