Is it normal for attic insulation to have a pebbly layer underneath the fluffy stuff?

Yeah, what you're describing sounds like vermiculite, and it was the go-to pour-in attic insulation around that era. It looks exactly like you said, little accordion-looking pebbles that pour like gravel. A lot of it came from one mine in Libby, Montana that was contaminated with asbestos, so there's a real chance yours has some, but there's no way to tell by looking at it. Some batches are clean, some aren't, even within the same house apparently.

For who to call, go with an accredited asbestos testing lab, not an insulation company. An insulation outfit that also sells removal has every reason to find a problem. A lab will charge you somewhere in the range of thirty to fifty bucks a sample and most will walk you through the sampling procedure over the phone. Follow their instructions on how to collect it since they usally want a specific amount in a sealed container, labeled with where it came from. One thing worth knowing about: there's a trust set up for this exact situation, the Zonolite Attic Insulation Trust. If your vermiculite traces back to the Libby mine, they reimburse a chunk of your testing and removal costs. A lot of people never claim it because they don't know it exists. Check their submission process before you pay a lab out of pocket, because they have requirements for how the sample gets handled and documented. If it does come back positive, you've got options besides full removal. Undisturbed vermiculite that's staying put under more insulation is generally considered safe to leave in place. The risk comes from stirring up dust, so until you get results, cut way back on trips up there and don't move any more of it around. If removal turns out to be neccessary, hire a licensed abatement contractor. It's not a DIY job, the disposal rules alone are a headache.

And keep the attic hatch closed and weatherstripped in the meantime. That's your best barrier between the attic air and the rest of the house.

I agree with the lab recommendation, beacuse while visual identification of the clay-like mineral chunks is helpful for preliminary diagnosis, only laboratory analysis can confirm the presence of hazardous crystalline silica or other toxic components. When you do go through with the sampling, ensure the technician collects material from several diferent layers, not just the immediate surface, to account for potential variability across the entire volume of the material. Furthermore, some labs require the sample to be sealed in a way that prevents any airborne particles from entering during transit to maintain the integrity of the test. I have seen documentation of specific procedures for crush samples versus loose particulates that need to be followed precisely.

I've been dealing with insulation too, but mine was old fiberglass batts in a different section of my place. It isn't the pebble stuff, of course. I'm wondering if the testing process is relly the same no matter what kind of material you have. I heard some labs only test for a few specific things, which feels like it might miss whatever is in the older materials. My neighbor who had their stuff looked at mentioned they needed a specific type of sample, maybe that's just normal procedure for anything they test.

The whole Zonolite Attic Insulation Trust thing seems like a massive bureaucratic headache. I highly doubt that reimbursement process is as simple as it sounds, especially for a homeowner who is already worried about this stuff. Dealing with a trust to pay for testing and removal feels way too complicated for a quick fix. I've dealt with similar old building issues and the paperwork and requirements usually outweigh any small financial help you get. Stick to getting the lab results first before you get caught up in these claims.