Distinguish among similar minerals: a. Both pyrite and chalcopyrite have a metal
ID: 1711909 • Letter: D
Question
Distinguish among similar minerals: a. Both pyrite and chalcopyrite have a metallic luster, a greenish-black streak, and no cleavage; they are heavy and can be very difficult to distinguish on the basis of color. If no crystals are visible, how would you tell them apart? b. Magnetite and hematite can both be dark gray to black and look similar. How could you tell them apart if you did not have a magnet? Hornblende and augite commonly are black, have the same hardness, and exhibit two directions of cleavage. They are difficult to distinguish when they occur as small crystals in a rock. What would you look for to tell them apart? c. d. Calcite, halite, and fluorite all have perfect cleavages, and they can all be the same color. How would you distinguish among them? e. Talc and serpentine can be the same color, have similar greasy to pearly lusters, and both can have a greasy feel. How do they differ? f. If chlorite and biotite occur as small crystals in rocks, it may be difficult to tell them apart. What properties might be helpful? g. What single property is most useful for distinguishing between potassium feldspar and plagioclase?Explanation / Answer
A. Pyrite has pale bass yellowish color while chalcopyrite has brassy golden yellow colour.
B. Magnetite has black streak and hematite has reddish brown streak. Hematite is a component of rust but magnetite is not.
C. Hornblende has very black shiny cleavage and long rectangular crystals while augite has duller black and not very reflective and cleavages and blocky crystals.
D. Calcite has rhombohedral cleavage while flourite and halite have isometric cleavage for the most part. Moreover flourite is harder than both other.
E. Talc is the softest mineral and serpentine is not.
F. Chlorite can be distinguished by its green colour and pleochroism from biotite.
G. Plagioclase has cleavage with striations and translucent while K-feldspar is usually opaque.