Crystallization and Element Compatibility

The lecture covers the concept of trace elements, their compatibility, and their role in crystallization and melting processes. It explains how trace elements differ from major elements, focusing on their behavior during crystallization and melting. The lecture also delves into partition coefficients, equilibrium, and fractional crystallization, as well as equilibrium and fractional melting, highlighting the differences and implications of each process.

What is the primary reason sodium and potassium are considered incompatible during mantle melting?

• They are too large to fit into mineral structures.

• They have a high melting point.

• They react with other elements to form new compounds.

• They are excluded from the mantle residue and enter the melt quickly.

Which of the following best describes a trace element?

• An element with a concentration greater than 1% in rocks.

• An element that controls the crystallization of minerals.

• An element with a concentration less than 0.1 weight percent in rocks.

• An element that forms the primary structure of minerals.

How does the ionic radius of an element affect its compatibility in a mineral?

• Ionic radius has no effect on compatibility.

• Compatibility depends on how closely the ionic radius matches the ideal size for a mineral site.

• Smaller ionic radii always decrease compatibility.

• Larger ionic radii always increase compatibility.

What is the main difference between equilibrium and fractional crystallization?

• Equilibrium crystallization involves the removal of crystals from the melt.

• Fractional crystallization allows crystals to adjust their composition with the melt.

• Equilibrium crystallization maintains a closed system where crystals and melt remain in contact.

• Fractional crystallization results in uniform crystal composition.

In the context of crystallization, what does a partition coefficient greater than one indicate?

• The element is incompatible in the mineral.

• The element is highly incompatible in the melt.

• The element is compatible in the mineral.

• The element is not present in the mineral.

What happens to the concentration of a highly compatible element in the melt as crystallization progresses?

• It decreases rapidly.

• It remains constant.

• It increases rapidly.

• It fluctuates randomly.

In equilibrium crystallization, how do the crystals and melt interact?

• They remain in equilibrium throughout the process.

• The crystals are isolated immediately.

• The melt is removed as soon as it forms.

• The crystals dissolve back into the melt.

What is a key difference between equilibrium and fractional melting?

• Equilibrium melting removes melt immediately.

• Fractional melting keeps melt in contact with the solid.

• Equilibrium melting keeps melt in contact with the solid.

• Fractional melting does not involve any solid.

During fractional melting, what happens to incompatible elements?

• They remain unchanged.

• They are removed from the melt.

• They are concentrated in the melt.

• They are concentrated in the solid.

How does the concentration of incompatible elements change during equilibrium melting?

• It decreases as melting progresses.

• It remains constant throughout.

• It increases as melting progresses.

• It fluctuates without a pattern.