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One such individual is Robert Gentry, who holds a Master's degree in Physics (and an honorary doctorate from the fundamentalist Columbia Union College).
This was never fully successful as the size/intensity of an observed damage halo was also a function of the abundance of radionuclides present in the inclusion, and the crystalline structure of the host mineral. First is his contention that the granitic rocks from which samples reportedly came constitute the "primordial" crust of the Earth.
Within these rocks are biotite (an iron-bearing form of mica) and fluorite crystals which bear a relatively uncommon class of tiny, concentric discoloration "haloes" (figure 2).
Sedimentary rocks are secondary in formation, being the product of precursor rocks (of any type).
Igneous rocks form from molten material, and are further subdivided into two main categories, the volcanic rocks which form from lava extruded at or near the surface; and plutonic rocks which form from magma, deep within the crust.
Gentry has spent most of his professional life studying the nature of very small discoloration features in mica and other minerals, and concluded that they are proof of a young Earth.