This specimen has a stalagmite of celestite - likely just clusters of smaller crystals growing over a larger one. The color is a delicate light-blue, and most of the damage is confined to the largest crystal at the base of the stalagmite.
Two large crystal dominate this Madagascar celestite specimen, and the largest (and best protected) has a nearly perfect outer portion (the base is cloudy). The next largest crystal has an appealing surface texture, and interesting growth patterns.
I am especially impressed by the largest crystal on this specimen (near the bottom center). It has a perfect shape, although the base has been partially cleaved off. It is also slightly darker and more transparent than the other crystals on the specimen.
Celestite is a favorite among mineral collectors.
Its sky blue (or celestial) color is very pretty, and is unique in the mineral kingdom.
Celestite also forms with other colorful minerals, making very nice combinations.
Blue Celestite with bright yellow sulfur is one of the most famous colorful combinations of minerals.
Celestite has the same structure as Barite
(BaSO4), and forms very similar crystals.
The two may seem identical by ordinary methods, but a flame test can distinguish them.
By scraping the dust of the crystals 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 with the flame and
produce those colors.
Normally barite is not blue, but many specimens of blue barite are often misidentified as celestite.
The nice crystals, good luster and attractive blue color make fine specimens of celestite an
outstanding mineral for someone's cabinet or display case.
Beautiful celestite geodes are found
Color is usually blue but can also be colorless, yellow and tints of red, green and brown.
Luster is vitreous.
Transparency crystals are transparent to translucent.
Crystal System is orthorhombic; 2/m 2/m 2/m
Crystal Habits include the bladed crystals that are dominated by two large pinacoid faces top and bottom and small prism faces forming a jutting angle on every side.
There are many variations of these faces but the flattened blades and tabular crystals are the most common.
If the pinacoid faces become diminished or are absent, the resulting prismatic crystal has a rhombic cross section.
This habit is rather common in specimens from Madagascar.
Also nodular, fibrous or granular.
Cleavage is perfect in one direction, less so in another direction.
Fracture is conchoidal.
Hardness is 3 - 3.5
Specific Gravity is approximately 3.9+ (above average for translucent minerals)