How to Identify Minerals Based on Streak Color

What characteristic can help in identifying minerals when rubbed against an unglazed porcelain plate?

a) Color
b) Hardness
c) Streak
d) Transparency

What mineral leaves a green-black powder when rubbed against an unglazed porcelain plate?

a) Galena
b) Hematite
c) Pyrite
d) Graphite

Explanation

When trying to identify minerals, one of the key characteristics to observe is the streak color, which is the color of the powder residue left behind when a mineral is scratched across an unglazed porcelain surface. Each mineral has a unique streak color that can aid in identification.

Among the options provided, galena leaves a dark-gray streak, hematite leaves a red-brown streak due to its iron(III) oxide composition, and graphite leaves a dark gray to black streak since it is made of carbon.

However, pyrite, also known as iron(III) sulfide (FeS2) or "fool's gold," is the mineral that leaves a greenish-black or brownish-black streak when rubbed against an unglazed porcelain plate. While it is typically described as dark, dull green without significant black tones, it closely matches the green-black description in the question.

Therefore, based on the likely discrepancy in color description and the typical results of mineral streak testing, pyrite is the correct answer for the mineral that leaves a green-black powder when rubbed against an unglazed porcelain plate.