He is deeply interested in the spiritual world.

We exist as a part of the material world.

In biology, a subkingdom is one of the large units in taxonomy.

The animal kingdom is incredibly diverse, and it is said that there are still species that have not been discovered.

The animal kingdom is known for its diversity and complexity.

This mineral has a very clear crystal zone.

The study of crystal classes is an important part of mineralogy.

Understanding crystal habit is important in understanding the characteristics of minerals.

This substance has the properties of a crystalloid.

This twin crystal has a very unusual shape.