Name (please PRINT legibly): _______________________________________________
Luster, Color and Streak
Color. Humans respond strongly to color, which can be a handicap when identifying minerals.
Some minerals have a characteristic color that is found in all specimens of that mineral, while the
color of other minerals is highly variable.
Color is a very complex phenomenon related to how white light is reflected, scattered,
transmitted, refracted or absorbed as it interacts with a mineral lattice. A mineral that absorbs
everything other than the blue part of the visible spectrum will have a blue color. A mineral that
does not absorb any of the light spectrum is white or colorless. A mineral that absorbs all of the
light spectrum is black.
Streak is the color of a fine powder of a mineral. For relatively soft minerals, the powder is
made by scratching the mineral specimen over a plate of hard, unglazed white or black porcelain.
The resulting “skid mark” is a trail of finely powdered mineral whose color is well displayed
against the porcelain. Some minerals have a streak color that seems to differ from their color in
hand specimen.
Luster. The luster of a mineral is related to how light is reflected or scattered by the mineral. If
a large percentage of the light is reflected, the mineral will have a mirror-like or metallic luster.
Lesser degrees of reflection result in submetallic and non-metallic lusters. Other luster terms we
will use include vitreous (glassy), earthy (dull luster of dirt or powder), silky (satin sheen due to
thin parallel mineral fibers), resinous, pearly (pearl-like luster), greasy (although solid, looks and
maybe feels greasy or oily) and adamantine (the brilliant luster of diamond).
Activity 2a. Some types of minerals always (or virtually always) occur in a single characteristic
color, as noted in the following table. Identify the 6 unknown minerals labeled #1c through #6c
using color as the primary criterion, but also using the table of mineral properties in your lab
book as needed to make your final interpretations.
#1: ________________________________
#2: ________________________________
#3: ________________________________
#4: ________________________________
#5: ________________________________
#6: ________________________________
ColorStreakLuster.docx
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Activity 2b. Some types of minerals have a distinctive streak. Identify the 4 unknown minerals
in boxes with streak plates that are labeled #1s through #4s, using streak as the primary criterion,
but also using the table of mineral properties in your lab book as needed to make your final
interpretations.
#1s: ________________________________ #2s: ________________________________
#3s: ________________________________ #4s: ________________________________
Activity 2c. Luster is one of the first things we notice in a mineral, along with its color.
Describe the luster of the specimens labeled 1L through 6L, using only the terms listed below.
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•
•
•
•
•
•
metallic
non-metallic (NM) – vitreous
NM – earthy
NM – silky
NM – resinous
NM – pearly
NM – greasy
#1L: ________________________________ #2L: ________________________________
#3L: ________________________________ #4L: ________________________________
#5L: ________________________________ #6L: ________________________________
ColorStreakLuster.docx
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