Question

Igneous rocks that cool more quickly have smaller mineral crystals, while igneous rocks that cool more slowly have larger mineral crystals.

How would a rock that formed from lava cooling on the Earth's surface compare with a rock that formed from magma cooling deep in the Earth's crust?

A. The rock that formed from lava would have larger crystals than the rock that formed from magma.

B. Crystal size would be very small and identical in both rocks.

C. Crystal size would be very large and identical in both rocks.

D. The rock that formed from lava would have smaller crystals than the rock that formed from magma.

Answer 1

Lava is a volcanic rock which cools above ground fairly quickly so it yields many small crystalline structures. Magma is plutonic and cools very slowly under the crust. So it yields few large crystals. That means the answer is D.

Answer 2

D. The rock that formed from lava would have smaller crystals than the rock that formed from magma.

Step-by-step explanation:

The volcanic rocks, effusive or, more rarely, extrusive are those igneous rocks that were formed by the cooling of lava on the earth's surface1 or magma (mass of underground molten matter) at shallow depths.

The rapid cooling of magma or lava that turns into volcanic rock causes many small crystals, also called microcrystals or fine grains, to form on these rocks. Rapid cooling can also form volcanic rocks composed entirely or partially of glass.3 The most common volcanic rocks on Earth are basalt followed by andesite, while other volcanic rocks are rhyolite, dacite and trachyte to mention a few. .

Volcanic rocks constitute a small part of the rocks that originate from magma. It is estimated that during the Cenozoic an annual average of 3.7 to 4.1 km³ of volcanic rocks have been generated on Earth, a much smaller amount than the 22.1 to 29.5 km³ of plutonic rocks that are believed to have formed on average annually in the same period of time. weather.