& Rab's question?

Sorry rab :-) [I'm scurrying around a bit and missed the simulpost] Yes - and to save further questioning - All of them
Bob - No

Raak - That's probably a bit too tangible for an 'abstract' :-)

I googled quincunx and was pointed to the Law of Error, none the wiser so I'm stepping back as its time for a Kit-Kat.

Interesting - you answered "no" to the question "Can it be heard?"

Inkspot - No
rab - Indeed I did. It was a specific question and I would have been misleading you if, at that time, I'd answered yes. However, as 'this' can be perceived by all the senses collectively, I answered yes. I feel it may be more helpful.
Boolbar - No, not really.

... but as I am continually astounded by your collective grey matter, I fully expect the answer to be here when I return this evening. Clue#3 - it has two sides - the one I'm thinking of is the happy/desirable side.

I keep not noticing earlier questions/answers - I do apologise, it doesn't indicate any contempt for fellow questioners/answerers on my part...

This summarises all that chalky answered before catching the train. I’ve taken out the wild guesses and repeated questions and added the clues at the end.

This is an * A B S T R A C T * thing.
It is (sort of) a human concept.
It can’t be heard.
Is it found in a book? Yes, but most things might, wouldn't you say?
It is common knowledge [but that's not the answer].
It is not commonly considered art.
It is not fictional.
It can be a saying or verbal expression.
Does it have to do with language? er ... No. It would be very misleading if I replied otherwise.
It is not directly something to do with the weather.
It is not an emotion.
It is not a feeling.
Does it have to do with music? – No.
Is it an action? - Not really ... it could be ... sometimes ... vague, sorry.
Nothing to do with water.
It is "not really" connected with the arts.
It would have been known about in 1900.
It is 'made' of abstract AND tangible things.
Is it a scientific theory or principle? - mmmm ... tricky. I shall say No, but your line of questioning might lead you to the right place.
It is not 'historically' attributed to one person.
It is not a religion.
It can exist/occur where there aren't any people around e.g. Mars.
Is it a rule or law? - Sort of, yes.
Is it anything to do with mathematics? - In a way, yes.
Is it possible for people to make one? - I think we've established that it's an 'it'.. therefore, it's a common perception that people can make 'it' - although they may not be aware they are.
It is not Gravity.
It is not Heat.
A quincunx? - What an interesting guess - it isn't correct but some might believe that the occurrence of such might have some bearing on 'it'.
Is it an effect rather than a cause? - It is both a cause and effect :-)
It can be perceived by any of the five senses.
It is not one of the seven deadly sins.
It is not a maze.
It is not the chaos theory.
Does it have something to do with the sun? - No, not really.
- Sorry - I've got a train to catch

[Clue #1] It is not an emotion but it can have an effect on the emotions.
[Clue#2] It is an 'it'.. therefore, it's a common perception that people can make 'it' - although they may not be aware they are.
“There are a whole bunch of questions that haven't been asked yet, which should simplify matters considerably”.

[Clue#3] - it has two sides - the one I'm thinking of is the happy/desirable side.

From all that, I interperet it as being a natural occurance or event, the quincunx which I interperet from a quick browse as illustrating 'randomness'(is this right), is the scientific/maths a blind alley which leads down to something measurable even on Mars

I suppose I should ask in case I suppose erroneously

Even if Boolbar is not right, its a damn clever answer.

rab - No, but getting closer
Boolbar - No, not exactly, but excellent guess. Winning could be considered a part of 'it'
Inkspot - No, but the portent itself has a connection
Kim - Not directly
Software - Yes
Dazed - No
Inkspot - Yes to 'occurring event' as for 'natural' - I would say more 'yes' than 'no', although the mathematics might prove otherwise [Clue#4]

..... that's close enough. The answer was 'serendipity' but as this one has dragged on for a couple of days now, it may be best to leave it that a combination of your two guesses will do nicely. [insert smiley face here] I'm pleased because I was a-rootin' an' a-tootin' for you. So whilst ...
*the audience whoops and hollers [and exhales a collective sigh of relief] and waves handkerchiefs and garters and all manner of private apparel for that vair vair clever Raak*

... I shall prepare myself for the possible questioning of some of my replies :-)

Congrats Raak, and about bl***y well time!

Inkspot: But perhaps not on the scale that those words suggest.

BTW, I've just realised that it can be VEGETABLE instead of MINERAL.

[Raak] Re 'good of man' - I meant the sort of tools that make killing machines - I should have been more precise

Point to rab. Next!

Oops, meant to include one of these:

---

Despite being sorely tempted by an abstract, I did one of those last time so I think it's only fair I plump for a more tangible MINERAL on this occasion. Guess away.

Stepped out of the office for a moment to talk to my boss. We were discussing an integral and he suggested a few times that I "take it up the imaginary axis" which, I'm sorry to say, had me in schoolboy-snigger mode.

[Boolbar] Yes.
[Chalky] Bits of it are. (Oh, how I hate giving extra information away...).
[Riff] Probably not.

I'm afraid I don't know.