What are dikes, sills, and laccoliths? What will be an ideal ...

[leo leo]

What are dikes, sills, and laccoliths? What will be an ideal response?

Question 2

What are pegmatites, and how do they form? What will be an ideal response?

[b614102004]

Answer to Question 1

Dikes and sills are tabular or sheet-like igneous bodies. Dikes are discordant (they cut across rock
layers), and sills are concordant (they parallel the layering in rocks). Laccoliths are sills that inflate,
causing the overlying rock to bow upward. A laccolith has a mushroom-like geometry.

Answer to Question 2

Pegmatites are composed of mostly felsic minerals, close in composition to granite. The minerals in
pegmatites are enormous, at least 1 cm across and up to many centimeters or even meters. Pegmatites
are found near large granite plutons and form from the water-rich magma that remains after most of
the granite crystallized. The water-rich magma travels through cracks and has time to cool slowly,
creating enormous minerals.