Why QUINOA, AMARANTH, and PURPLE CORN were sacred to the INCAS?

Quinoa, Amaranth, and Purple Corn were sacred to the Incas because they were extremely rich sources of Iron, Copper, Manganese, and Zinc. They had the highest contribution to mineral intake to the human body.
They were considered sacred given the fact that because of their highest content of minerals, their use in rituals facilitated the transition of movements of sacred energies along the ceques (energy points).
They considered them a gift from the Creator (Viracocha). Through its consumption the cleansing of the negative energies were performed prior the engagements of rituals forming a strong and  clear path of communication between energies coming from the cosmological plane and the earth.
The Incas developed a unique culture that unified Nature and People together into the same fabric of life.
The bond made between earthly and spiritual realms was meant to be there and never be broken.
Purification and working with a clear mind and sincere heart were essential in asking the spirit of the land to provide for the people.
They kept the belief that if you do things in a very good way, good things were meant to follow. If carefully attention were not established between the planes, the result were expected not to be good. War and Famine would appear as a direct consequence from the negligence performed by the unclean ones.
Energy Vortices or Sacred Sites filled with subtle and concentrated energy were located at various geophysical places along the Inca Empire.
It was stated that crystals and minerals were a direct connection to the balance of the energy's lines of the Earth's plane and responsible for maintaining the stability of the earth, and at the same time maintaining the correct magnetic vibration in connection with the planets in the Universe.
The importance of the maintaining a proper harmony of planet Earth in relation to the Sun and Moon was sacred.
The misuse of personal power and misuse of crystals and improper cleansing of the physical human body were instrumental in their beliefs for the demise of their empire.