Anyway, the problem is that there are four separate material gradings for raw materials.
The original "geological" grading was introduced in Horizons in 2.0 and determines which planets have which materials. This only has four grades. All planets have all G1 (except metal-rich, which only have Iron and Nickel). They then have 3 G2, 2 G3 and 1 G4 - the 3-2-1 rule of early planetary exploration. This was nice and simple.
When engineers were introduced in 2.1 data and manufactured materials had five grades, so Frontier "spread out" raw materials over five grades as well for engineers. So the engineering grading system has five grades of raw materials - G1 is the same, G2 is some of the G2 geological, G3 is a mix of G2 and G3 geological, G4 is a mix of G3 and G4 geological, and G5 is the remaining G4 geologicals. Generally the materials which end up higher than their geological grade are the harder ones to find (Arsenic is G3 engineering) for various reasons. Frontier considered redoing the planetary materials so that the geologic grading was 5-grade as well, but explorers noticed in Beta and complained about it a lot, as it invalidated all their previous surveys (and this was before 2.2 made surveying easier, so to find out what materials a planet had you had to land on it and shoot a lot of rocks)
In 3.0, Frontier introduced material traders. Because of how they work, they need a rectangular block of materials - a requirement never envisaged for the original raw materials ... but there were only originally 5 G1 materials on the geological scheme, and lots of G2 materials. Neither existing scheme was suitable. To beat the raw materials into a rectangular shape with minimal deviation, Frontier:
- used the geological scheme as a basis
- added three mining-only raw materials (Rhenium and Lead at G1, Boron at G3) ... a way to add new ones without breaking the 3-2-1 rule.
- moved Selenium from G2 to G4 (the material trader massively overpays for it)
So at this point, there were three separate schemes, introduced at different times for different valid reasons, and not reconcilable. Unfortunate, but not really fixable without doing something more unpopular (invalidating old exploration data, making engineering harder by replacing easyish G4 raws with G5 manufactureds, or inventing a
lot of extra mostly useless raw materials to take up space on the trader grid)
But... for no obvious reason, the
display grade of a material in the right panel of your ship doesn't consistently use any of these schemes. Polonium and Technetium are both G4 geologic and trade, G5 engineering ... but Polonium is G5 right-panel and Technetium is G4. Zirconium is particularly bizarre - G2 geologic and trade, G3 engineering, but somehow ends up as G4 right-panel. This one is hopefully just a bug.
Fixing the display grade to be one of the other grades (I think the "trade" grade would be the best choice) would at least make things a bit clearer.