Physical Weathering:
* Frost Wedging: If water seeps into cracks and freezes, it expands, putting pressure on the rock and eventually breaking it apart.
* Thermal Expansion and Contraction: Fluctuations in temperature can cause the rock to expand and contract, leading to weakening and eventual fracturing.
* Abrasion: Wind-blown sand or water carrying sediments can scrape against the rock surface, causing erosion.
Chemical Weathering:
* Hydrolysis: Water reacts with certain minerals in the metamorphic rock, breaking them down into new compounds. This is particularly effective on feldspar minerals, which are common in many metamorphic rocks.
* Oxidation: Oxygen in the air reacts with minerals like iron, forming iron oxides (rust). This weakens the rock and gives it a reddish color.
* Carbonation: Carbon dioxide dissolved in water forms carbonic acid, which can dissolve certain minerals, especially carbonates like calcite.
* Biological Weathering: Plants, lichen, and other organisms can release acids that break down rock. Roots can also physically wedge rocks apart.
Outcomes of Weathering:
* Formation of Sediment: Weathering breaks down the metamorphic rock into smaller pieces, ultimately contributing to the formation of sediment.
* Soil Development: Weathering releases minerals and nutrients into the soil, making it fertile for plants.
* Changes in Rock Appearance: Weathering can alter the color, texture, and shape of the metamorphic rock.
* Exposure of Underlying Rocks: Weathering can remove the outer layers of the metamorphic rock, revealing the underlying rocks.
Specific Examples:
* Marble: This metamorphic rock, primarily composed of calcite, is susceptible to carbonation, causing it to dissolve and create sinkholes.
* Slate: This metamorphic rock, formed from shale, is generally resistant to weathering, but its layering can make it vulnerable to frost wedging.
* Gneiss: This metamorphic rock, with its distinct banding, can weather along its layering, leading to the formation of slabs or blocks.
Ultimately, the weathering process transforms a metamorphic rock into something new: smaller fragments, soil components, or even a completely different rock type.
