Need help shooting close pictures of gemstones. What i do wrong?

Hello, for a small shop im trying to open (selling gemstones) i decided to shoot some photos of the gems i have. I bought a lightbox (LED) and i use my Canon Powershot sx60. The problem is however, that the pictures i make are not great. Even if i compare them to my iphone + zoom gadget i bought for 3$, the powershot pictures look far worse. What is the correct technique? Should i use the zoom function or put the camera very close? I feel that when using zoom the quality gets worse. Hope to get some tips!! Please check my pictures here: http://imgur.com/a/IeRvc