Quote from Shadow World MA 3rd Edition :
Eog-Black (5000 sp): Can inhibit or even nullify all non-Dark Essence in the same way White Eog inhibits Evil Essence. For general properties see Grey Eog, below.
Eog-Grey or ‘common’ (2000 sp): An extremely hard metal, it is brittle in its pure form, but when combined with certain other elements the resulting alloy can be used to make superior weapons and armor. It is enchanted, and ‘common’ Eog has a dull silvery luster. An addition, certain pure types of Eog have the power to locally inhibit the Flows of Essence (see black and white types).
Eog-White (5000 sp): Can limit the powers of Dark Essence (e.g., Essence originating from the Unlife or dark gods or their minions). Eog’s inhibiting power varies with the amount and proximity, but a small chamber lined with White Eog panels 1˝ thick would prevent all but the most powerful Evil magicians from casting a spell. Note that, while a Magician inside this chamber would have trouble casting spells, his Power Points are not actually drained.
Indicative prices are in sp per ounce of material. Interestingly, density is not provided, so there is no way to compute volume from mass or vice versa. Good luck finding the price of those 1" thick panels :p