Rapidcreekite
Chemical formula: Ca<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)(CO<sub>3</sub>)·4H<sub>2</sub>O
A rare hydrated calcium sulfate and carbonate, forming delicate, acicular crystals or chalk-like coatings.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous to Silky, Dull
- Streak
- White
- Density
- 2.47
- Cleavage
- Perfect on {100}, Good on {010} and {001}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Characteristic features of rapidcreekite are its typical forms of occurrence (radial aggregates of white needles), very low hardness (2 on the Mohs scale), and violent reaction with dilute hydrochloric acid (effervescence). Its occurrence in association with other rare phosphate and sulfate minerals from Yukon is also a strong diagnostic clue. ## Distinguishing from Similar Minerals Rapidcreekite is sometimes confused with other white minerals with an acicular habit. It is distinguished from gypsum by its reaction with acid. Aragonite, which also reacts with acid, is much harder (3.5-4). Other similar minerals, such as natrolite or scolecite, do not react with acid and have different formation environments. Final confirmation often requires chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal Forms Crystals are elongated, acicular, or flattened (bladed), usually not exceeding a few millimeters in length. They form characteristic radial or fan-shaped aggregates, as well as fibrous aggregates, spherical aggregates, and earthy coatings.
Geological environment
## Genesis Rapidcreekite is a secondary mineral, forming in the oxidation zones of deposits at low temperatures. It forms as a result of weathering and alteration of earlier minerals under specific geochemical conditions. In its type locality, it formed in voids and fissures within formations composed of siderite and quartz. ## Mineral Associations This mineral co-occurs with other secondary minerals. In Yukon, its typical associated minerals are gypsum, aragonite, kulanite, wardite, lazulite, quartz, and siderite. ## Localities The most important and well-known locality of rapidcreekite, from which the best collector's specimens originate, is the Rapid Creek and Big Fish River area in Yukon Territory, Canada. This is its type locality. It has also been reported in several other places around the world, including Germany, but these occurrences do not provide material of collector's significance.
Rarity
Rare
For collectors
## Quality Criteria The most highly valued rapidcreekite specimens are those that display well-formed, sharp, and lustrous crystals gathered in rich, radial aggregates, contrasting with the dark matrix rock (most often siderite). The size and aesthetics of the entire aggregate, as well as the absence of damage to the delicate needles, are crucial for the collector's value of the specimen. ## Popular Localities The vast majority, if not all, rapidcreekite specimens available on the collector's market come from one location: the Rapid Creek area in Yukon Territory, Canada. This is the classic and only significant locality for this mineral.
Care and storage
## Cleaning Rapidcreekite specimens are extremely delicate and brittle. They should only be dry-cleaned, using a soft brush to remove dust or blowing it off with a photographic air blower. Any contact with water or mechanical cleaning can irreversibly damage the crystals. ## What to Avoid Avoid contact with water and all chemicals, especially acids, in which it rapidly dissolves with the release of carbon dioxide. The mineral is very soft, so it must be protected from scratching and any impact. Storage in a humid environment can lead to its degradation. ## Storage It is recommended to store specimens in closed, padded boxes (e.g., "micromount" type) that protect them from mechanical damage, dust, and humidity changes. Do not expose it to direct sunlight or in places with fluctuating temperatures.