Invisible played some heavy progressive rock en Español, out of Buenos Aires from 1973-1977. First let's get to the singles.
"La llave del mandala" (The Key to the Mandala), 1974 single
That's actually their 2nd single, but I like it better anyway. Definitely in the proto-hard rock realm of yer Deep Purple's and such.
"Estado de coma" (Coma), 1974 single
[***NSFW VIDEO***] Similarly, but moreso...
Invisible disco completo (1974)
The album sounds quite different than the harder singles - more often proggy & jazzy. And I think they made the right call. Not sure if their heavy boogie-rocking would carry over through a whole LP. Here's a cleaned-up translation from the YouTube description...
Note from Rolling Stone's 100 best albums of rock bands:
After the end of Pescado Rabioso [Rabid Fish] in late 1973, [Luis Alberto] Spinetta formed Invisible with Pomo [Lorenzo] and Machi Rufino Lorenzo (the former from Pappo's Blues), and the following year released his debut LP, with the drawing "Puddle" by M.C. Escher, on the cover. Complex music (composed rhythmic, jazz harmonies) and lyrics influenced by Surrealism and the French Symbolists characterized this first group stage, which shows Spinetta's expansive creativity that would not fit on one record, as evidenced by three singles appearing in the same year: "La llave del mandala", "Elementales leches" and "Viejos ratones del tiempo."
These additional tunes all end up as bonus tracks in various places, but my favorite bonus so far is the "Mandala" B-side.
"Lo que nos ocupa es la conciencia, esa abuela que regula el mundo" (What concerns us is the consciousness, that grandmother that regulates the world), 1974 b-side
RAWK!! Now I want to get that 7" single on vinyl! And possibly the full-length as well...
Here's some English-language band info (& en Español). By the way, I know there are more than 2 countries in South America.