"Wheels of Light" by Rosalyn Bruyere

I have extracted some parts of this outstanding book that deal with the Third Eye / Sixth Chakra.

Here are some 6th Chakra correspondences:
color: purple
body: celestial
gland: pineal
animal: archetypes; all spirits, living and dead
element: radium
gemstone: alexandrite
contains: inspiration; insight
people: spirit teachers; spiritual friends
(p.42-43)

Rosalyn Bruyere calls the subtle body that corresponds to the 6th Chakra as "the celestial body," the one that holds our individual future and is also our access to that future (p.46)

The term "celestial" derives from antiquity where it was believed that the future existed in space and that one day each of us would die and become a "star," thus returning to the divine celestial light from which we had come. However, this would not occur until we had accumulated enough light [enlightenment] to illuminate a section of heaven. (Manly P. Hall, "Secret Teaching of All Ages.") The celestial body is that realm of light; and being associated with illumination, this body influences all that light enables us to "see." Put another way, the celesrial body allows us literally to "see the light." It is the realm of "sight" in all of its various manifestations: clairvoyance, visualization, insight, foresight, inspiration, psychic phenomena, and finally physical manifestation itself (from the thought, dream, fear, or other feeling to physical reality. (p.47)

The evolutionary cycle is reflected in metaphysical doctrine...[it] was known to the Native Americans and symboliozed by them in the chakra system...the lower chakras are aligned to animal forms. The first chakra is the snake, the second chakra is fish, the third chakra is bird or fowl, the fourth is mammal, and man resides in the fifth center. The sixth chakra takes man one step further into the collective and the spiritual, since...it is aligned with all spirits, living and dead...(p.53)

the sixth chakra is located between the brows. (p.69)

when a stimulus comes into the body it is registered in the first chakra [as] a change in [its] electromagnetic field...producing an energy flow...into the second...energy then continues to flow into the sixth chakra...From antiquity this center has been cloaked in "mystery." Nearly everyone would agree that there is nothing mysterious about physical sight: the eyes see. For some, psychic sight may seem mysterious, but it is not. The third eye also sees; it allows us several kinds of perceptions. It provides the means by which we perceive extrasensorily. It should also enable us to see "what is so," not just what is ours. We as a people tend to "see" or "take in" what is in our own energy flow, what is reflected from our own field, what is on our own path. We do not often see a complete picture but instead focus on individual rather than universal problems. As a result, we continue to "see through a glass darkly" [1 Cor. 13:12] The third eye allows us a clearer, more expansive vision. After entering the Third Eye, the energy flow touches the pituitary gland, reflects off the pineal gland, and mushrooms out through the top of the crown . This pattern holds if energy is allowed to flow up and out. However, if one chooses to do anything with the energy, the flow will reflect off the pineal and then hit the pituitary, after which it will continue its movement out through the third eye, where manifestation can occur. The ancient Egyptians symbolized this movement in their image of a cobra poised and ready to strike , head expanded. (p. 69-71)