Can anyone identify the film/TV I`m thinking about?

Maybe "Quatermass 2" where the aliens are inside tiny black capsules? Cant remember a pile in the movie, but the hiss, as they open and attack the humans.

Could be the Hammer film 'X the Unknown' (1956). Could also be a 60s British SF film called 'Night of the big heat' (1967).

Your description sounds like my Aunt Doris's rhubarb crumble.

Was there any thick, oozing yellow stuff?

Yeah its definitely ESCAPE INTO NIGHT, based on the book MARIANNE DREAMS by Catherine Storr. Only show once in about 1969 then the tapes were destroyed. But a black and white copy has been found and recently released on DVD. Absolutely loved this show as a kid.

Actually, Quatermass (1979) has several scenes which fit that description, as the people who gather at the megaliths are wiped out, left as ashes, and the entire site is covered in a fine whitish dust, with steam coming off the stones.

Late to the party, but I can definitively state that this movie is, indeed, "Monolith Monsters", 1957, which scared the crap out of me back then. I could have written your post for you, as all the points you make match my own. I did some research into '50s Sci-fi several years ago ... and there it was, together with "Tarantula", "The Mole People", "The Incredible Shrinking Man" and "Monster on Campus" (All available in the "Classic Sci-fi Collection"). They're all a little corny now, but remain eminently watchable - nostalgia ain't all bad!

There is real life ... and then there are movies!

the Monolith Monsters