The Barite Group of Minerals
(Photos above are all Barite.)
The barite group is composed of minerals with a similar orthorhombic structure and related chemistry. It is named for its most common member, barite. The general formula for this group is A(SO4). The A can be either barium, lead, or strontium. Some of the sulfur is replaced by chromium in the rarest member of the group, hasemite. This is a small group with only four recognized minerals, but it is an important group because the three most common members are all ores of their respective metal ions. The structures of these minerals are rather similar and therefore they form similar crystal habits.
The following are the more common members of the Barite Group of Minerals:
Anglesite (Lead Sulfate)
Barite (Barium Sulfate)
Celestite or celestine (Strontium Sulfate
Hashemite (Barium Chromate Sulfate)
Barite
Barite is a common mineral and makes very attractive specimens. It often is an accessory mineral to other minerals and can make a nice backdrop to brightly colored crystals. At times bladed or tabular crystals of Barite form a concentric pattern of increasingly larger crystals outward. This has the appearance of a flower and when colored red by iron stains, these formations are called "Desert Roses". Because Barite is so common, it can be confused for other minerals. Celestite (SrSO4) has the same structure as barite and forms very similar crystals. The two are indistinguishable by ordinary methods, but a flame test can distinguish them. By scrapping the dust of the cystals into a gas flame the color of the flame will confirm the identity of the crystal. If the flame is a pale green it is barite, but if the flame is red it is celestite. The flame test works because the elements barium (Ba) and Strontium (Sr) react in the flame and produce those colors.
See http://mineral.galleries.com/minerals/sulfates/barite.htm
Be sure to view the great discussion on orthorombic structure.
Here are the photos again:
Anglesite:
Barite:
Celestine:
Hashemite: No photos available at this time.
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