Valerie creates a model using three different rocks. the rocks are classified as igneous, metamorphic, and sedimentary.
which property does valerie use for classification purposes?
color
formation
shape
texture

Texture

Explanation:

Geologists done use color formation or shape to classify.

As a geologist I can tell you that this is a lie, but listen to the book.

The correct answer is on the basis of their formation.  

Explanation:

The formation of igneous rocks takes place by the cooling of the molten rocks or magma. The formation of sedimentary rocks takes place from the sediments, that is, when they solidify, or through cementation or weathering on the Earth's surface. The formation of metamorphic rocks can take place from both sedimentary and igneous rocks through the changes taking place in them because of pressure and heat within the Earth.  

answer: a. a gene that causes a specific trait.

weathering is the answer.