here’s some background information and speculation, as someone not involved in the industy. the silicon wafers used for making chips are big single crystals, which are made by the Czochralski method the crucible is also made of silica and needs to be very perfect, so that no crystals are seeded from the walls, so it makes sense to me that the crucible needs to be at least the purity of the desired silicon wafers - which is at least 99.9999% pure and for research-grade samples 99.99999999% pure. I suspect that the leading-edge nodes requires the high-end of this scale. Its economical to start with the highest purity material that you can, which according to Conway’s Material World comes from spruce pine, but its possible to use a lower grade starting material.