I was not referring to your example.
This beach is blessed with a pure white sand that stretches for miles.
I'll point out to you that sand is a mass noun, not an abstract noun.
It's an uncountable noun. That's the topic.
Yes, it's not an abstract noun. If it were, it would not be a counterexample to your claim that it's ok to use the indefinite article "only before abstract nouns."
To argue against that statement, one would have to produce an uncountable noun (such as sand), that was not abstract, and which could take an indefinite article - which I had done even before you made the claim.
In your example, sand is being modified by adjectives that permit an indefinite article such as a to be used.
So, you agree that your statement that you can only do this with abstract nouns has exceptions (or is wrong) - for example, when there are adjectives qualifying the uncountable noun?
Furthermore, the initial sound of pure requires an a rather than an.
Yes, I would agree with that. Was that in contention?