The character 珉 from the original phrase is said to mean "an apple of Sodom"...is that true? If so, what does that even mean? I though the character 珉 meant a jade-like stone as it has the particle 王 = 玉 (jade).
珉 is beautiful and looks like
玉, it's still stone.
故虽有珉之雕雕,不若玉之章章 means, even
珉 is beautiful and has high value to be engraved (to artwork), it's still not as clear and beautiful as
"珉" is some kind of stone which looks similar to "玉" (Jade).
"雕雕" means dedicated craftsmanship and implies external appearance, impression, etc.
"章章" means the natural color (usu. white or red) and implies the internal character, virtue, etc. of a gentleman (君子)
In the phrase you quoted, 孔子 concluded that 玉 was better praised than 珉 not because of rareness, but rather its characteristics similar to gentlemen (君子).