The Hardest Naturally Occurring Substance on Earth

I've also wondered how soft vinyl can wear out a diamond. Other than random diamond particles in the environment or contaminating the vinyl itself, shouldn't the diamond last forever? Of course that theory doesn't pan out because we know very well that diamond styluses do indeed wear out with use. I am reminded that the Grand Canyon was all carved from stone with water.

Diamonds .. huh..
I always thought the hardest natural thing on Earth was my ex mother in laws heart. Maybe I was wrong, as there’s been a lot of pubs (public bars) in Australia selling beers reportedly as cold as ex mother in law's heart..

Diamonds you say, well then..okay

And diamonds are forever, that’s nonsense eh?

Here's another spin on how something soft can wear something much harder.  A carbon steel blade used to chip tree limbs will last a very long time happily turning hundreds of yards of fresh cut tree limbs into mulch.  Now replace the blade with a new, identical one and feed it only tree tops with lots of large leaves and the blade will dull much quicker.

When the moving blade passes the softer leaves, the leaves can slide perpendicular to the edge of the blade before and as it's being cut.  When this rubbing occurs, it dulls the edge sooner that the harder wood that maintains it's shape and is cut by the blade pretty much inline with the path of the blade's edge.  

Add some dirt to the mixture and the sliding, rubbing action across the edge of the blade really dulls things up in a hurry. 

Since the stylus is sliding past the two sides of the record album at pretty much a perpendicular angle to the groove walls, you have the same dynamics.  As other's have pointed out, the actual pressures involved at this microscopic level is quite amazing.  Add even a little dirt and its just a matter of time, (or distance - traveling in the record groove - depending on how you want to look at it).

Water, a relatively soft substance, carves out large structures and even large canyons from solid rock, a relatively hard substance. You know, like Monument Valley and Grand Canyon. Rivers, rainfall: erosion! 🤗

Start wearing a hat in the rain. It's obvious by your posts, your brain is eroding.