GG5: 	a precious stone; a jewel; a gem.
中辞典: a precious jewel [gem].
Koj, Daijr, etc. say much the same.

I can't see any emphasis on it being spherical.

@@ -12,0 +13,2 @@
+<gloss>precious stone</gloss>
+<gloss>gem</gloss>

https://kotobank.jp/word/宝玉-627338

貴重な玉。宝石。宝珠
The fact is a 玉, also checking 宝珠 which is defined in terms of 宝玉, both seems to stress the fact 宝玉 is a "spherical object" - the current definition is failing to convey that