41. Alabaster and softer kinds of serpentine, all about 3 on the Mohs scale , are more durable than soapstone. 42. Each crystal chosen has a hardness level of 6 or higher on the Mohs scale [ of mineral hardness ]. 43. On the Mohs scale of mineral hardness, quartz rates no higher than a 7, less for types with impurities. 44. At its softest, calcium carbonate can form in concrete as chalk ( of hardness 1.0 on Mohs scale ). 45. This mineral ranks a 5 on Mohs Scale of Hardness, though it is considered brittle, exhibiting conchoidal fracture when broken. 46. Changbaiite has a hardness of 472.4 kg / mm 2 on the Vickers hardness scale and 5.3 on mohs scale . 47. Donnayite ranks at a hardness of 3 on Mohs scale and has fair to imperfect cleavage on the c-axis { 001 }. 48. Due to the fact it can be readily scratched with the finger nail, its hardness is ranked at about 2 on the Mohs scale . 49. It has a metallic luster, a hardness of 274 on the Vickers scale and a hardness of 4.5 on the Mohs scale . 50. The Mohs scale article implies that a finger nail has an absolute hardness of about 6, and that iron has an absolute hardness of 21.
