Cavansite vs. Pentagonite

Mineral(s): Cavansite (left image) / Pentagonite (right image)
Locality: Wagholi Quarry, Pune District, India (for both)

Here I contrast two similar yet different minerals: cavansite on the left, and pentagonite on the right. The canvansite here is just a group of radiating clusters nearly 2 cm wide. The pentagonite specimen is a nearly 3 cm crystal cluster. You certainly cannot make an identification through color alone. They both also share the orthorhombic crystal system. Both are silicate minerals, specifically phyllosilicates ("sheet" silicates). They're popular minerals amongst collectors, but many are easily confused. So what's the difference?

There are several differences actually. One way to look at it is how aggregates of crystals form. Cavansite tends to grow in ball-like clusters (spherules) with crystals often grouping together fairly tightly, while pentagonite starts off as a rounded cluster but ends up growing crystals in more distinct, individual blades (crystals tend to be more free-standing).
Another way to make a comparison is how an individual crystal forms. Looking closely, an individual cavansite crystal very often forms with flat terminations, while pentagonite typically forms with pointed terminations.
Cavansite is more common in the market, while pentagonite is rarer and are more highly valued. It is also suggested that cavansite forms at low temperatures, while pentagonite forms at higher temperatures (therefore, it is uncommon for both minerals to be present within a single specimen).

If you ever come across these beautiful blue minerals, take note of this (bring a hand lens if you have one!) and see what you're really looking at. It is extremely common for dealers to misidentify them. Nowadays, particularly for canvansite, these minerals go beyond serving as mineral specimens. They're incorporated into jewelry, pendants, and more. Once unknown, they're now popular minerals.