Bonemold
Also known as 'Great House' armor in Morrowind, bonemold is a medium weight armor affordable only by Dunmer nobles. Each piece is assembled from many pieces of softened shell, molded into shape, then bonded and reinforced with resin glues.The Bone books are wrong, since they're foremost a tall tale.
... or just imitations of the original Skar-style designed to resist ash storms?
Yes.
http://www.imperial-library.info/mwbooks/great_houses.shtml are designed in the Dunmer village style, built of local materials, with organic curves and undecorated exteriors inspired by the landscape and by the shells of giant native insects.
What the heck to Guar subsist on in the ashlands?
Um. Er. Scrib.