It's a plain old piece of sandstone....
You can see by the mis-shapen line at the "bottom" of the so-called "triangle", that it's not "man-made"... And in the side views, you can see that it is made up of layers - though they're a bit difficult to see, if a person isn't familiar with that kind of rock.
I have pieces like that all around my house, in the river-rock landscaping...
If you wish, try rubbing the stone with your fingernail or a piece of metal - you'll probably see that grains of sand are dislodged...
It is the WRONG KIND OF ROCK for arrowheads...
Arrowheads, spear-heads, and the like are made out of rocks like obsidian, chert, agate, and even some quartzites - if they are firmly consolidated, could be shaped into weapon-heads...
But not this thing. It's too soft; won't break with a "conchoidal" fracture (like glass, for example), and wouldn't even begin to hold together long enough to become a spear-head, let alone withstand an impact with a large animal, especially if it happened to hit a bone lying just under the skin...
Not to mention; it'd never survive the "knapping" process - or wouldn't produce the extremely sharp edges that a "knapped" piece of glass-like rock [the aforementioned obsidian, chert, agate, jasper, and so on] will produce, if handled properly.
Throw that at a woolly Musk Ox - on the head of a spear, and you'd just make it mad....
Zid