Mineral necessarily constant for all sides, which is a function of its structure; crystallographic weakness renders some directions softer than others. An example of this property exists in kyanite, which has a Mohs hardness of 5½ parallel to [001] but 7 parallel to [100]. The most common scale of measurement is the ordinal Mohs hardness scale. Defined by ten indicators, a mineral with a higher index scratches those below it. The scale ranges from talc, a phyllosilicate, to diamond, a carbon polymorph that is the hardest natural material. The scale is provided below: Lustre indicates how light reflects from the mineral's
Abenakiite-(Ce) Abenakiite-(Ce) Abenakiite-(Ce) (IMA1991-054) is a mineral of sodium, cerium, neodymium, lanthanum, praseodymium, thorium, samarium, oxygen, sulfur, carbon, phosphorus, and silicon with a chemical formula NaCe(SiO)(PO)(CO)(SO)O. The silicate groups may be given as the cyclic SiO grouping. The mineral is named after the Abenaki, an Algonquian Indian tribe of New England. Its Mohs scale rating is 4 to 5. Abenakiite-(Ce) was discovered in a sodalite syenite xenolith at Mont Saint-Hilaire, Québec, Canada, together with aegirine, eudialyte, manganoneptunite, polylithionite, serandite, and steenstrupine-(Ce). Combination of elements in abenakiite-(Ce) is unique. Somewhat chemically similar mineral is steenstrupine-(Ce). The hyper-sodium abenakiite-(Ce) is also unique in