Question

think critically 5. speculate why there are almost no extrusive ultrabasic rocks in earth’s crust.

Explanation:

Ultramafic (ultrabasic) rocks are high - in - magnesium and iron. They have high melting points. They tend to crystallize and solidify at depth in the mantle before they can reach the surface to form extrusive rocks. Also, when they do start to rise, they may react with other materials in the crust, altering their composition.

Answer:

Ultramafic rocks have high melting points and tend to solidify in the mantle before reaching the surface, and may react with crustal materials during ascent.