From what I've little research I've done, besides making a pretty green stone and in rare cases green crystals, it seems that it's usually powdery in form and is an indicator of nickel ore. Keeping this in mind, it may be something akin to the corrosion of the ore like rust on iron or the green on copper. I don't really know of any practical uses though unless you are into stone or crystal healings, but that's not my arena of knowledge or research. I hope this helps out.

1. 2nite

2. abderite

3. abelite

4. abietite

5. acanthite

6. accite

7. aceite

8. achondrite

9. aciculite

10. aconite

11. acquisite

12. acrite

13. actinolite

14. adamite

15. adamsite

16. adiaphorite

17. aerolite

18. aerosiderite

19. agagite

20. agalmatolite

21. aikinite

22. albertite

23. albite

24. alexandrite

25. allanite

26. allochroite

27. almandite

28. aluminite

29. alunite

30. amalekite

31. amazonite

32. amblygonite

33. ambrite

34. ammite

35. ammonite

36. amorite

37. amosite

38. ampelite

39. amphibolite

40. amphitrite

41. anabolite

42. analcite

43. anchorite

44. andalusite

45. andesite

46. andosite

47. andradite

48. anglesite

49. anhydrite

50. ankerite

51. annabergite

52. annamite

53. anorthite

54. anorthosite

55. antholite

56. anthophyllite

57. anthracite

58. anthraconite

59. anthropolite

60. anthropomorphite

61. anthropophagite

62. antigorite

63. antilewisite

64. antimetabolite

65. antimonite

66. antisatellite

67. antisemite

68. antlerite

69. antothite

70. apatite

71. aphanite

72. aphrite

73. aphrodite

74. aplite

75. apophyllite

76. apotactite

77. appetite

78. apposite

79. aragonite

80. archimandrite

81. arenicolite

82. arenite

83. areopagite

84. arfvedsonite

85. argentite

86. argillite

87. argyrodite

88. arkite

89. arragonite

90. arsenite

91. arsenopyrite

92. artotyrite

93. asphaltite

94. asterophyllite

95. astroite

96. atacamite

97. attapulgite

98. attrite

99. atwite

100. augite