Good Friday. Was it ?
1) FIBONACCI : (on,FBI)*,ac(-------c)i- : not usually thrilled about 'quite' used like this but today is fine because the clue is very good. A nicely integrated definition.
6) PITTA : hm(pitter) : never seen the gadget as my olives are usually on a pizza. Having said that, is it not the worst feeling EVER crunching an olive one doesn't expect is intact ? Feels like all your teeth have crumbled.
9) INHUMAN : in(Hum-)an : of Hume and Hovell fame. Thanks Mrs Geraghty of the 2nd Grade.
10) BRACKET : b(rack)et : the definition is a little undercooked.
11) ZLOTY : crypdef : a Polish bank would be a 'Pole vault'. What about 'Pole vaulter's gold' ? As zloty apparently means 'golden'. I would've accepted 'vaulter' as a bank worker because it was amusing. Better surface too.
12) PETRICHOR : pet,(rich),-or- : evidently it's a real word for post-rain freshness.
13) TOOTLES : tootles- : no horn, so it's toot-less.
15) HUMMUS : hum,mus- : ie must.
18) WEBCAM : W(be<)C,a-------m : pretty good.
19) LYCEUMS : (my,clues)*
22) SECTARIAN : sec,t(ari-)an
23) POSER : ddef : pretty good.
24) IRONMAN : iron,man
25) TIMPANI : tim(pan)i- : ie timid.
26) ASKIN : -askin- : ie basking.
27) PACHYDERM : (my,red,chap)*