The most common and most likely answer to this crossword clue is the 6 letter word MARVEL
I've seen this crossword clue in Independent
M
A
R
V
E
L
More clues leading to the result MARVEL
Buddy explains!

The straight part
We know that "Miracle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case miracle = marvel.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MARVEL mean?
MARVEL noun- That which causes wonder; a prodigy; a miracle.
- Wonder, astonishment.
- To become filled with wonderment or admiration; to be amazed at something.
- To marvel at.
- (used impersonally) To cause to marvel or be surprised.