Have you spoken to your contractor and fabricator about this?

I'm no stone expert, but we did something similar with our maple island counter. I suspect maple is a fair bit lighter than quartz and ours was not easy to do (we ended up with what I think is called a piano hinge that runs the entire length and then a specially built support that can retract). In hindsight, I would have just had it built as a solid unit b/c we rarely have down.

Is it possible to do safely? Probably. Is it possible to do safely and cost effectively? Probably not.

I don't like this idea.

Create a WOOD hinged "gate" instead. A thick oak board intended for a step or thresh hold would work,l however, if you want a truly beautiful and interesting "gate", consider having one custom made by those craftsmen that create custom cutting boards and tables, often from "used" wood.

https://www.google.com/search?biw=1326&bih=617&tbm=isch&sa=1&ei=d7L2XbujEo6isAXrxYyIDw&q=custom++wood+tables+and+cutting+boards+northeast+georgia&oq=custom++wood+tables+and+cutting+boards+northeast+georgia&gs_l=img.12...22768.26545..28206...1.0..1.206.1628.18j0j1......0....1..gws-wiz-img.1Kq6SB3iPas&ved=0ahUKEwj7urPl2LjmAhUOEawKHesiA_EQ4dUDCAY#spf=1576448663328. 

You are indeed correct that quartz is too heavy to be hinged, especially safely and securely.

What about something fabricated out of stainless steel?

First, there are hinges that hold multiple tons, any machine shop on the planet can fabricate a hinge that will easily hold a quartz countertop. The hinges on a forklift trailer are rated to about 15,000 lbs across 24". I assure you that quartz is not too heavy to hinge.

Just about any machine shop could fabricate the plate steel, weld the hinges on and have it ready for epoxy and fasteners in a couple of days. It will cost a decent amount because everything this custom always does.

Having said that, there are two glaring problems with this plan. First, it is going to be just butt-ugly. You are going to have to have supports that hold the counter up when in the down position that are just going to be sitting there with nothing on them when the counter is up and fairly visible and thick hinges that there is no way to hide when the counter is up or down.

Additionally, you are going to have to add hydraulic lift assists to keep from cracking the counter when you accidentally drop it down. This is not going to add to the beauty of your kitchen at all. In the end, it is just a bad idea. If you really want a backsplash you are much better building in a hydraulic lift for one. Some variation of this...

Consider a two level island instead. It is certainly possible to do what you want but it would be expensive as you would be paying for design time in addition to the custom fabrication.

A rangetop on an island without a permanent counter zone of safety behind it is a big safety issue. You wouldn’t be able to leave it in the down position, and not risk injury. Island cooking already has enough logistics and added expense issues without doubling that for something so unattractive and awkward. And unsafe.

You wouldn’t be able to leave it in the down position, and not risk injury.

I assume that the OP is talking about hinging up rather than down since they want to use the counter as a backsplash when not in use as a counter.

I have no idea what you want to do maybe post a picture of your idea as for hinging there is a big difference when making a hinge for a piece of metal that can be welded there is no way to weld quartz and IMO a weird idea as far as I can imagine

What do you mean be a backsplash for your range Top?

It's taken me a while to visualize what you're asking.....are you saying that your cooktop will be in an island and you'd like the stone to hinge up to be a backsplash at certain times and flatten out sometimes to be a bar overhang? Seems ill-advised to me.

If you're worrying about not having a backsplash for an island cooktop, the more appropriate solution would be to move the cooktop off the island.

Really I just don’t get it . You need a backsplash behind your range all the time and I have no idea how that would become a bar

I have no idea what you want to do maybe post a picture of your idea as for hinging there is a big difference when making a hinge for a piece of metal that can be welded there is no way to weld quartz and IMO a weird idea as far as I can imagine

I apologize for not offering a more detailed explanation, sometimes I assume certain common understandings or experiences that may not be present.

You can't add point hinges to granite...period. You would be concentrating the entire load on a few points which would cause the granite to fail. You would have to add the hinges to plate steel that runs practically the entire length of the granite. There are various ways to hide the plate steel but there is no way to avoid some mechanism to distribute the point load to a wider surface. Technically plate steel is not your only option, it is just the only one that is easily hidden.

I know this is an older post but I am a commercial millwork estimator and have come across the so called "countertop lift hinges" that this OP is likely thinking of. There were hinges called Lift-A-Syst and they did make some that could support quartz countertops but the models were anywhere between $1500-$2000 for just 1. However, this manufacturer stopped making these hinges and the ones still on the market like Sugatsune I don't believe are made to lift quartz. A lot of the times restaurants that have these lift hinges for their tops and quartz tops actually end up having to do a laminate that matches the quartz in order to make use of these hinges. Also, these hinges are bulky and not the best looking, and of course do get worn out eventually. Do you really want these hinges to get worn out and possibly drop the heavy top?

I secretly roll my eyes when I see these countertop lifts in architectural drawings for multiple reasons, especially the practicality of servers having to lift up a 60lb quartz top if it's 3/4" thick or even a 125lbs countertop if it's 1 1/2" thick when carrying food and drinks all in the name of supposedly maintaining countertop space. Right, because telling a customer to move their plate, silverware, and themselves out of the way every time the server has to get out from behind the bar is real convenient for anyone... a swinging door in this case is much more practical. I promise you that you won't miss the whopping 36" of countertop space by doing this... or the sprained wrists.