That looks like nephrite, a type of dark jade. Nephrite is very good for all kinds of kidney complaints. Metaphysically, it's good for anything to do with growth, but also with emotion and with good elimination and purification (if you need to purify something in your mind, heart or soul, use nephrite).
The clearer and lighter jade is China's most noble and spiritual stone, as well as one of the most beautiful stones on this planet. Legend has it that jade was created of the tears of a dragon, the great creative animal. There are not enough words in English or characters in Chinese to speak of its qualities. Here are some:
- wisdom
- moderation
- prosperity
- luck
- benevolence
Here's a quote from the Zhou Li, 2,500 years old:
Anciently superior men found the likeness of
all excellent qualities in jade. Soft, smooth and
glossy, it appeared to them like benevolence;
fine, compact and strong, like intelligence ... its
flaws not concealing its beauty, nor its beauty
its flaws, like loyalty; with internal radiance
issuing from it on every side, like good faith.
Jade is mentioned in the 50th Hexagram of the Yi Jing, to signify something has transformed into the greatest possible good. So to work with jade is very special.