You may be thinking about Schubeck Lifters, later bought out by Smith (Not related to Ckay Smith.)
The lifters had some sort of a super hard composite, maybe ceramic, type puck glued to the bottom of a hydraulic lifter body. I don't recall if the solids had a "puck" or were made entirely of that material. They worked well as long as you had roller-type spring pressures in the valvetrain to prevent any type of valve float or lofting on your flat tappet cam. They allowed steeper ramps and as advertised, they seemed to polish the lobes rather than wear them. I swapped cams & lifters without concern about mixing or break-in! But I was still careful. Lash had to be kept to a minimum as well. That's because the impacts eventually shattered the "puck" and sent tiny shards of the diamond-hard material throughout the engine. That turned off a lot of people because they lost engines because of it. Others haven't had a problem. I personally ran 200lbs on the seat and near 400lbs open up to 7000 rpm in my Dart. But I'm not sure if that was good enough or if it really needed more, like some others had.
Schubeck sold the business to someone named Smith, but I don't know if Smith is still in business. I haven't heard anything about those lifters in a while. Some pop up for sale once in a great while.
