Ancylite-(La)
Chemical formula: LaSr(CO<sub>3</sub>)<sub>2</sub>(OH)·H<sub>2</sub>O
Ancylite-(La) is a rare mineral from the carbonate group, forming small, prismatic or dipyramidal crystals with colors ranging from yellow to brown.
Properties
- Mohs hardness
- 4-4.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.89-4.15
- Cleavage
- Good on {110}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identifying ancylite-(La) in the field is very difficult due to the small size of its crystals and its resemblance to other minerals. Key features include the characteristic crystal shape (short prisms, dipyramids), relatively high density for a carbonate, and occurrence in specific geological environments. Definitive identification requires advanced analytical methods, such as X-ray spectroscopy (XRD, EDS). ## Distinguishing from Similar Minerals Ancylite-(La) can be confused with other minerals from the same group (e.g., ancylite-(Ce)), as well as some other rare earth carbonates, such as bastnäsite or parisite. Distinguishing them with the naked eye is practically impossible and requires chemical analysis to determine the dominant rare earth element. It differs from calcite or dolomite by its significantly higher density and crystal form. ## Crystal Forms It forms short, prismatic crystals, often terminated by steep pyramids, which gives them a pseudo-octahedral appearance. Crystals can be slightly rounded or distorted. It also occurs in radial, spherulitic, and rosette aggregates.
Geological environment
## Genesis Ancylite-(La) is a hydrothermal mineral. It forms in the late stages of crystallization in alkaline pegmatites, carbonatites, and in alpine veins cutting metamorphic rocks. It forms as a result of the interaction of solutions rich in rare earth elements and carbon dioxide with surrounding rocks. ## Mineral Associations It often co-occurs with other rare earth element-bearing minerals. Typical associated minerals include: ewaldite, burbankite, calcite, quartz, microcline, albite, titanite, aegirine, and other minerals from the ancylite group. ## Localities The most important and classic occurrences of ancylite-(La) are: - Kola Peninsula in Russia (Khibiny and Lovozero massifs), where it occurs in nepheline syenite pegmatites. - Mont Saint-Hilaire in Quebec, Canada - known for its well-formed microcrystals in syenites. - Ilimaussaq igneous complex in Greenland. - Langesundsfjord district in Norway.
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp, and undamaged crystals, even if they are small. An intense, saturated color and attractive placement of crystals on the rock matrix, creating contrast, are important. Specimens from classic, historic localities, such as Mont Saint-Hilaire or the Kola Peninsula, are particularly sought after. ## Popular Localities Specimens from Mont Saint-Hilaire, Canada, are considered the global standard for this mineral due to their perfect crystal forms. Samples rich in rare earth minerals from the Russian Khibiny and Lovozero massifs are also highly prized.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. The use of water is not recommended due to the mineral's potential solubility and sensitivity. ## What to Avoid Contact with acids must be strictly avoided, as they cause rapid dissolution with the release of carbon dioxide. The mineral is relatively soft and brittle, so it should be protected from impacts and scratching. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in stable conditions, in closed boxes or display cases, to protect them from dust and mechanical damage. It is best to keep it away from harder minerals.