I understand that colons can join two independent clauses if the second independent clause expands on or explains the first. I understand that semicolons can join two independent clauses if they are closely related in subject matter. What I do not understand is why so many grammar guides online say that the colon and the semicolon are in no way interchangeable.
For example, this following sentence is from the novel God's Demon by Wayne Barlowe:
'Adamantinarx was not dissimilar, in its composition, from many of the cities of Hell; its flagstoned streets ran red with the blood of its souls, its soul-bricks sighed and blinked as one passed them, and its countless low buildings groaned and shuddered like any others in any other infernal city.'
The second independent clause in this quote both expands on the first independent clause AND is closely related to the first independent clause in terms of subject matter; thus, could the semicolon not be replaced with a colon? In this instance, are the colon and the semicolon not interchangeable?
The reason I'm asking is because I'm a writer who consistently has to choose between a colon and a semicolon for the purpose of joining two independent clauses, however, in a lot of cases, they seem interchangeable, such as with the above example.