Which statement accurately describes slate formation?

Which statement accurately describes slate formation?

• A. Slate formed from sandstone under high heat and pressure.
• B. Slate is formed from shale under heat and pressure without melting.
• C. Slate is formed from limestone in acidic conditions.
• D. Slate is formed from granite under pressure.

Answer: (B)

Slate formation is a result of metamorphism acting on shale. When shale is subjected to heat and directed pressure, the fine clay minerals realign into a parallel, platy arrangement without melting, giving slate its characteristic slaty cleavage and very smooth, planar surfaces. This low- to medium-grade metamorphism preserves the solid state, distinguishing slate from rocks formed by melting. If the parent rock were sandstone, the high heat and pressure would more likely produce quartzite, not slate. Limestone under metamorphism becomes marble, not slate. Granite under pressure tends toward a higher-grade foliated rock such as gneiss, not slate.

Slate formation is a result of metamorphism acting on shale. When shale is subjected to heat and directed pressure, the fine clay minerals realign into a parallel, platy arrangement without melting, giving slate its characteristic slaty cleavage and very smooth, planar surfaces. This low- to medium-grade metamorphism preserves the solid state, distinguishing slate from rocks formed by melting.

If the parent rock were sandstone, the high heat and pressure would more likely produce quartzite, not slate. Limestone under metamorphism becomes marble, not slate. Granite under pressure tends toward a higher-grade foliated rock such as gneiss, not slate.