this link gives full detail: the link
Galena is a common and popular mineral for rock hounds. Its characteristic cubes, distinctive cleavage and high density make it easy to identify and a favorite in high school geology labs. The structure of Galena is identical to that of halite, NaCl. The two minerals have the same crystal shapes, symmetry and cleavage. Some Galena may contain up to 1% silver in place of lead. The large volume of Galena that is processed for lead produces enough Silver as a by product to make Galena the leading ore of Silver.
PHYSICAL CHARACTERISTICS:
Color is lead to silver gray sometimes with a bluish tint.
Luster is metallic to dull in weathered faces.
Transparency crystals are opaque.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include the cube, octahedron and combinations of the two. Spinel twinning is possible forming flattened crystals. Also massive and granular.
Cleavage is perfect in four direction forming cubes.
Fracture is uneven and rarely seen because of the perfect cleavage.
Hardness is 2.5+
Specific Gravity is approximately 7.5+ (heavy even for metallic minerals)
Streak is lead gray
Associated Minerals are calcite, dolomite, sphalerite, pyrite and other sulfide minerals, also lead oxidation minerals such as cerussite and anglesite.
Other Characteristics: brighter metallic luster on cleavage surfaces than on crystal faces.
Notable Occurances include Texas-Oklahoma-Missouri area, USA; Germany, Peru, Mexico, Zambia, and England.
Best Field Indicators are crystal habit, cleavage and, perhaps most importantly, density.