1. Master the characteristics and visual identification methods of this kind of common minerals;
2. Understand the relationship between the morphology and physical properties of minerals and their composition and structure;
3. Grasp the relationship between optical properties of minerals;
4. Be familiar with the classification and main physical properties of these minerals.
Second, difficulties.
Understand the physical properties of this mineral.
Three. Content, methods and tips
(1) practical specimens
① Realgar (2 1 18) ② orpiment (2 1 19) ③ Cinnabar (2 107) ④ chalcopyrite (2 108).
⑤ pyrrhotite (211)⑤pyrite (220 1) ⑦ arsenopyrite (2203) ⑧ porphyrite (2 1 10).
(2) Key contents and identification method tips
1. Classification of sulfide and similar composite minerals
These compounds are compounds of a series of metal elements with sulfur, selenium, tellurium, arsenic, antimony and bismuth. According to the characteristics of anions, this category can be divided into three categories:
(1) Simple sulfide: anions are simple ions S2-, Se2-,Te2-,As2-,etc. Such as galena PbS, chalcopyrite CuFeS2, nickel-nickel ore, etc.
(2) For sulfides, anions are diatomic ions formed by the combination of two atoms with valence bond of * * * *, such as [S2] 2-, [ASS] 2-, [SE2] 2- and so on. , such as pyrite Fe [S2] and arsenopyrite Fe [Ass];
(3) Sulfide salt: the anion is a complex anion composed of semimetallic elements As, Sb, Bi and S, such as tetrahedrite Cu 12 [Sb4S 13].
Among them, simple sulfide and sulfide are common and important, and these two minerals are collectively referred to as sulfide; Sulfur salts are not necessary, but their concepts should be understood.
2. Physical properties of sulfide minerals
The cations that make up sulfides are mainly copper-type ions and some transition ions close to copper-type ions, and their elemental electronegativity is greater than other cations. Compared with other anions, anions S, Se, Te and As have larger radii and lower electronegativity, so there is little difference in electronegativity between anion and cation.
Because the electronegativity of the anions and cations of sulfide minerals is not much different, generally less than1(about 0.7), and the contact force between them and electrons is very small, when this factor plays a leading role and the cations are metals, sulfides with metal bonds are formed, such as PbS, Fe [S2], CuFeS2, Cu5FeS4, Sb2S3 and Fe [Ass].
Due to the strong polarization of copper-type ions, some semi-metallic elements are nonmetals with large anion radius and great deformability. When this factor plays a leading role, sulfides with valence bonds of * * * are formed, such as As2S3, AsS, HgS, ZnS, etc. Mineral diamond-like, translucent, with light or colored stripes, cleavage developed, and poor electrothermal performance.
Sulfide contains neither glassy minerals nor minerals easily soluble in water, which is completely different from typical ionic compounds. They are also different from the typical atomic lattice or metal lattice.
For example, although many sulfides have metallic luster, they are brittle and often have perfect cleavage, which is also hard for sulfides; Although some sulfides have diamond luster, they have little hardness and low melting point. Therefore, the lattice of sulfide can be regarded as a transition lattice.
The hardness of simple sulfide minerals is lower than that of cutting tools, because the anion radius is large and the cation electricity price is low, so the ion potential is not high; Such as PbS, ZnS, CuFeS2, etc. Or although the cation electricity price is relatively high (valence 3 ~ 4), the mineral lattice has a layered or chain structure, with strong intra-layer or intra-chain bonding, but weak inter-layer and inter-chain bonding, such as MoS2, Sb2S3, As2S3, etc.
Whether the simple sulfide with metallic luster develops cleavage depends on the type and strength distribution of chemical bonds in the structure; Simple sulfide with diamond luster develops well and cleaves; No sulfide cracking.
Among sulfides, only sulfide minerals have higher hardness, generally higher than knives. This is because sulfur anion not only has stronger internal binding force, but also has greater deformability than single sulfur ion, which greatly shortens the distance between sulfur ion and cation, which is 8% shorter than that of simple sulfide. Therefore, the arrangement of particles in sulfide is more compact than that in simple sulfide, and its hardness is significantly increased.
The relative density of sulfide is generally large, mostly above 4. For simple sulfide, its relative density mainly depends on the atomic weight of cation; For example, the relative density of ZnS is 4. 1, and that of PbS is 7.5; The relative density of sulfide is mainly determined by the packing density of internal particles, for example, the relative density of Fe [S2] is 5 and that of arsenopyrite (Fe [Ass]) is 6.2.
3. The secondary change of metal sulfide minerals and its geological significance.
The development and evolution of everything follows the laws of dialectics, and under certain conditions, unfavorable factors can also be transformed into favorable conditions. In the process of weathering, the destruction of surface sulfide forms a large number of sulfate solutions containing metal cations. When they penetrate into the reduction zone below the groundwater surface, they undergo further reduction reaction with primary sulfide, forming secondary sulfide-rich zones, such as the formation of chalcocite and celestite, thus greatly improving the industrial value of primary sulfide deposits.
Taking chalcopyrite as an example, the zoning, composition and significance of weathering crust are dissected and understood.
In the case of sufficient oxygen:
A concise course in mineralogy
In the case of insufficient oxygen:
A concise course in mineralogy
It can be seen that the primary metal sulfide deposit is weathered and leached, and under the reduction condition, secondary sulfides such as chalcocite and celestite are generated, which significantly increases the copper content of the primary deposit and reaches the mining conditions for industrial utilization. So the reduction zone is also called
It is a secondary enrichment zone, and the "iron hat" and malachite on the surface are the prospecting indicators of secondary sulfide deposits.
4. Identification method suggests that special attention should be paid to the differences of listed similar minerals in observation operation. In addition, the color of actinides often appears on the surface of bornite, so we should pay attention to it.
Copper red is its own color, its hardness is less than that of a knife, and its score is bright (malleable).
Four. Operation 1. Observe and describe the exercise specimens and master their identification methods. The contents, sequence and format of records are as follows:
A concise course in mineralogy
2. Distinguish the following similar minerals
(1) galena, stibnite and graphite: morphology, hardness, cleavage, relative density, KOH reaction.
(2) Chalcopyrite, pyrite and pyrrhotite: color, hardness and magnetism.
(3) Graphite and molybdenite: color, stripe color and relative density.
V. Thinking about problems
1. Summarize the classification and main physical characteristics of sulfide minerals.
2. The structure of galena and pyrite is similar (NaCl type), but the symmetry type is different. Why?
3. What are the uses of pyrite and chalcopyrite? What are their secondary products? What is the geological significance?