"Self" is the basic unit of being. That doesn't mean beings are singular, it means beings are multiple but that this multitude is always somehow unified with-in-as itself.
Self means that of a multitude or plurality of different things it can also be said of them, "these are one thing". The "one" doesn't come at the expense of or opposition to the "many", rather one and many are both the case and at the same time. And yes even rocks have this logical structure.
The fact that such structures act to persist as what they are, that their structure as "simultaneously one and many" is such that it moderates and modifies and selects interactions with what is not-itself in order to attempt to cause itself to endure rather than cease to exist, is what it means to say that "a rock self-values".
What we call the self-valuing of living things, or conscious things, such as ourselves, is basically an extension of that same self-valuing that things like rocks also have. We are a more derivative, complex and dependent iteration and expansion of the same underlying logically principle and mechanism as much simpler and "non-living" things as rocks.