What rock is this?

With the recent threads touching on mineralogy and with a resident geologist, I think I’ll bring up this point of curiosity I’ve had for a while.

Where I live here in South Carolina there is pretty much only one type of rock, but it is ubiquitous–you can’t dig a hole without almost immediately hitting a piece of it, ranging anywhere from pebble size to bigger than your head.

It is made up of large (around 5 mm or so) irregular grains of a mostly translucent white material with occasional more transparent grains that I’ve always assumed to be quartz. The grains are fairly loosely connected, and the outside (and sometimes spaces between the grains) are stained red (possibly from the red clay soil.) As a child, I used to enjoy taking the larger rocks and smashing the grains apart with a hammer. More recently, I’ve gathered them to use around plant beds. The example in the center of this crappy phone photo is roughly head-sized. The example in this flat-bed scan is small enough to grasp in a fist.

To my inexpert eye that’s probably nothing more exotic than granite, in which the pinkish parts are feldspar, the clear/smoky parts are quartz.

Can’t think of anything else it could be but granite, but an odd one for me. I don’t see any dark minerals (amphibole), which are almost ubiquitous in granite.

Also not an expert.

It’s impossible to tell what that is from those photos. Could be quartz-rich granite, could be a really coarse-grained orthoquartzite, could be some sort of clean metaconglomerate. Could you perhaps take a photo of a fresh (broken) surface? Pictures of weathered rock surfaces are near-useless for accurate identification. Include a pencil or coin in the photo for scale.

Diagnostically, I usually expect to see some clearly defined crystals of feldspar in a granite, in addition to the dark accessory minerals nachtmusick noted (they don’t have to be amphibole, around here they’re biotite). However. feldspars weather fairly easily to clay minerals, so a fresh surface helps a lot. I’m definitely seeing a lot of quartz, the conchoidal fracture is quite evident.

Or you could give us a rough idea of where in South Carolinayou are…

Have only a crappy camera phone available at the moment, but before and after and after and after. My location is pretty close to the center of the Sixmile thrust sheet (within 5 or so miles of the center of totality of the upcoming eclipse.)

I’ll be honest, it’s still hard to tell from those photos, but it looks like a quartzite to me.

Or on the outside, it could be some carbonate - but I’m sure I saw some conchoidal fracture in your first pics. Don’t suppose you have any acid handy?

The photos don’t show this clearly, but the rocks consist of fairly loosely-bound grains (as I mentioned, around 5 mm plus or minus) and when struck shatter something like safety glass.

Quartzite, then.