1977-D Washington Quarter (Probable PMD)

{Foreword} I'm new here and this is my first post. I read the guidelines and posting rules and did my best to be within standards for this post. If I've duffed something, please let me know and I'll correct it going forward. Now for my question:

{Post} I got this little guy as change the other day. I figure it for environmental damage, acid contact or some other type of PMD. I'm very much a novice and don't own a scale to weigh the quarter but it's noticeably thinner and more lightweight than the 1972-P in the last photo of a side by side. Seems like most of the cladding has been dissolved or removed somehow.

I'm just curious if any of you know what might've caused this poor quarter to lose its silvery luster and look so much like a copper penny? I'm more of an enthusiast than a collector but I've just never personally come across one so completely stripped of its cladding. I think I see pitting which made me think it might have possibly come into contact with an acid of some sort, maybe even intentionally. Could it be that or possibly something else?

I'm just trying to educate myself about coinage in general and you all seem to be a great community of folks with tons of experience and knowledge. I appreciate any ideas or thoughts any of you might have.