A Tessin crystal is a crystal that exhibits a unique growth pattern known as the Tessin habit, characterized by a hexagonal prism that continuously narrows towards its tip. This distinctive shape is formed by the regular alternation of steep rhombohedral and m prism faces.
Understanding the Tessin Habit
The Tessin habit is a specific crystal growth form, most notably observed in quartz crystals, where the typical prism shape is modified to create a tapering effect. This name originates from the Swiss Kanton Ticino, also known as Tessin, reflecting its historical observation or prevalence in that region.
Key Characteristics of the Tessin Habit:
A crystal displaying the Tessin habit can be identified by the following features:
- Tapering Shape: The most defining characteristic is its overall conical or pointed appearance, as the hexagonal prism gradually becomes thinner towards the crystal's termination.
- Alternating Faces: This tapering effect is not smooth but results from the precise arrangement of two different types of crystal faces:
- Steep Rhombohedral Faces: These are typically triangular or diamond-shaped faces that define the pointed termination of a crystal. In the Tessin habit, they contribute to the continuous narrowing.
mPrism Faces: These are vertical faces characteristic of hexagonal prism crystals. Their interaction with the rhombohedral faces in an alternating pattern creates the unique tapering.
- Mineral Association: While the concept describes a habit, it is famously associated with quartz crystals, which often display a wide variety of growth habits.
The Tessin habit illustrates how specific growth conditions and the interplay of different crystal faces can lead to remarkably distinct and aesthetically pleasing crystal forms.
| Feature | Description |
|---|---|
| Defining Shape | Hexagonal prism that continuously tapers or thins towards the tip. |
| Forming Faces | Achieved by the alternation of steep rhombohedral faces and m prism faces. |
| Nomenclature | Named after the Swiss Kanton Ticino (Tessin). |
| Common Mineral | Most notably observed and described in quartz crystals, although the habit can theoretically occur elsewhere. |
