What is "Pitdas Kush"?
Rashi: It is a gem, like "Odem Pitdah" (on the Choshen).
Malbim: It is so esteemed, that one would not set it in Kesem Tahor 1 (pure gold), for it is so superior. Even so, Pitdas Kush cannot be used to evaluate Chochmah!
It seems that this is not Pitdah of the Choshen, which was set in gold! (PF)
What is "Kesem"?
Rashi: It is a collection of gems for women's ornaments, like "Nezem Zahav va'Chali Chasem."
Rashi: Some say that it is a crown 1 .
Ibn Ezra: Kesem Tahor must be gold, like Zahav Tahor. If it were a gem, "Tahor" would not apply!
Rashi: This is wrong. We never find a verb form of Kesem, like we find regarding Keser - Machtir, Kosaros.
