"Ka'annahunna al-yaqutu wa al-marjan" (As if they were rubies and coral), meaning: the clarity of the ruby within the whiteness of the coral.
﴿كأنهن الْيَاقُوت والمرجان﴾ يُرِيد: صفاء الْيَاقُوت فِي بَيَاض المرجان.