I've encountered the following sentence in a game:
時には後ろを振り返ると案外役に立つ事がコロッと転がってたりするもんだ。
First, I'd like to understand why the "to" in コロッと isn't in katakana like the rest of the word, why the dictionary writes it all in hiragana (http://jisho.org/search/korotto). Maybe I got the wrong word?
But regardless of that, how do I put that part of the sentence into words? I seem to have it in my mind, but can't quite say it in english.
This コロッと isn't really describing the quality of the thing itself, I mean, it is, but much more reflecting the speaker's impression or observation.
In your example, 転がっている alone can fully depict the situation, "it's lying on the ground". The remainder, コロッと and ～たりする both represent the speaker's mood.
コロッと implies (of course not round or rolling-ness here) something exists there as casually, unattendedly as a roadside pebble. In other word, it's actually a rhetoric attributing one's failure to notice to that innocent thing.
たりする is a worth learning colloquial idiom that derives from たり of probability or exemplification. It means "sometimes could happen/do", "do — or something" or "things such like — happen".
That 「と」 must be written in hiragana because it is a particle. You have no choice here.
The 「と」 turns the preceding word 「コロッ」 into an adverb form so that it can modify the verb phrase 「[転]{ころ}がってたりする」.
「ころっ/コロッ」 is a colloquial and onomatopoeic "word"; therefore, it is not very important whether you write it in hiragana or katakana. You have a choice here. Your preference can be fully reflected in its orthography.
My own TL attempt for:
「コロッと[転]{ころ}がってたりするもんだ。」
would be:
"one might find (helpful things/items) lying about (unexpectedly)"
"(to your surprise) you may find (helpful things/items) just scattered about "
It’s hard for me to translate 案外役に立つ事がコロッと転がってたりする into Japanese, but I take it in the meaning of “You’ll find something lying before you just casually, which turns out to be helpful to you later in an unexpected way.
コロッと is a colloquial variation of コロリと. コロリ is an onomatopoeia or ideo-phone to describe the status of something / someone dropping, falling, or slipping down, like コロリと転ぶ。
と is a postpositional particle to link コロリ and 転ぶ. It’s not a part of コロリ or コロッ.
Onomatopoeias as a particle, like キャッキャ、ポキポキ、ドスンドスン are more often than not described in カタカナ、but と used as a particle shouldn’t be described in カタカナ.
