サッと: Mix of ひらがな and カタカナ in the same word?


So, I've come across this sentence

> そのとき、陽が当たった石版に何かの影がサッと横切った。

which I'm fairly sure it means something like

> At that time, something's shadow quickly crossed the sunlit lithograph.

Now, what surprised me was the word サッと. I know that カタカナ is sometimes used to
emphasise the word (much like an italic or bold font). What I didn't know is
that there are words written in a mix of ひらがな and カタカナ.

A quick search revealed
[this](https://japanese.stackexchange.com/questions/15199/are-there-words-
which-consist-of-katakana-and-hiragana-letters-together) answer. From what I
could surmise, three groups of words were mentioned:

  1. When the final word is made of two other words (e.g. あんパン is made from joining あん and パン)

  2. Foreign words made into verbs (e.g. ググる from ググル, ダブる from ダブル), in which a final る is written in ひらがな

  3. The same concept as 2. but for adjectives (e.g. セクしい from セクシー)

Now, サッと doesn't match neither group. From the context of the sentence, I've
connected it with 颯っと which is usually written in kana alone, according to
[Jisho](https://jisho.org/search/%E9%A2%AF).

In summary, why the mix of ひらがな and カタカナ in this case?




Onomatopoeic words can generally function adverbially with or without と.
However, for onomatopoeias ending in 〜っ, と is usually added.

Onomatopoeias can be written either in _hiragana_ or in _katakana_ , but as is
common for grammatical particles the と will usually be written in _hiragana_.

See also

  * [What is the purpose of adding と?](https://japanese.stackexchange.com/q/24943/1628)
  * [What does "fūtsu" mean?](https://japanese.stackexchange.com/q/28525/1628)
  * [Does anyone knows the meaning of "モゾリと"?](https://japanese.stackexchange.com/q/59771/1628)
  * [What does どぼり mean?](https://japanese.stackexchange.com/q/59632/1628)




Onomatopoeic words can generally function adverbially with or without と.
However, for onomatopoeias ending in 〜っ, と is usually added.

Onomatopoeias can be written either in _hiragana_ or in _katakana_ , but as is
common for grammatical particles the と will usually be written in _hiragana_.

See also

  * [What is the purpose of adding と?](https://japanese.stackexchange.com/q/24943/1628)
  * [What does "fūtsu" mean?](https://japanese.stackexchange.com/q/28525/1628)
  * [Does anyone knows the meaning of "モゾリと"?](https://japanese.stackexchange.com/q/59771/1628)
  * [What does どぼり mean?](https://japanese.stackexchange.com/q/59632/1628)

