In most cases, they are not. English has at least a half-dozen completely different -en suffixes.
The one you are thinking of is the one that the OED says is
added to noun-stems to form adjs. with sense ‘pertaining to, of the nature of’.
In Teut. the adjs. so formed chiefly indicate the material of which a thing is composed. Of the many words of this formation which existed in OE. scarcely any survive in mod. use; but the suffix was extensively applied in ME. to form new derivatives. Some of these took the place of OE. words, from which they formally differ only by the absence of umlaut; compare OE. gylden with mod.Eng. golden, OE. stǽnen (early ME. stenen) with ME. and dial. stonen, made of stone. From 16th c. onwards there has been in literary English a growing tendency to discard these adjs. for the attrib. use of the sb., as in ‘a gold watch’; hence many of them have become wholly obs., and others (as golden, silvern) are seldom used except metaphorically, or with rhetorical emphasis. It is only in a few cases (e.g. wooden, woollen, earthen, wheaten) that these words are still familiarly used in their lit. sense.
However, there are quite a few other -en suffixes, none of which are really productive any longer:
- Create diminutives like chicken, kitten, maiden.
- Create feminines like vixen.
- Create plurals like oxen, brethren, children, kine.
- Create verbs from adjectives, like darken, deepen, harden, madden, moisten, widen. This one is moderately productive insofar as words like lengthen, strengthen, hearten are of relatively recent vintage.
- Create past participles like broken, spoken, sunken.