Characteristics and origin of polycrystalline dolomite needles in the Triassic Jialingjiang Formation, Upper Yangtze Platform, southwest China
✍ Scribed by Zhu Jingquan
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 597 KB
- Volume
- 118
- Category
- Article
- ISSN
- 0037-0738
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✦ Synopsis
Abnormal elongate crystal morphologies of dolomite are extensively distributed in the Triassic Jialingjiang Formation, Upper Yangtze Platform. The dolomite crystals, here termed polycrystalline dolomite needles (or PDN), are not elongated monocrystals, but are a polycrystalline assemblage formed by contiguous growth of several rhombohedral monocrystals. The extension direction of PDN is at right angles to the crystallographic c-axis of the dolomite monocrystals. PDN occur primarily in lithofacies rich in grains and consequently rich in primary pores, and appear to form during early diagenesis. Previous observations on fibre and dendrite calcite crystals, and their close morphological similarity suggest that PDN may have formed by way of pseudomorphous replacement (or dolomitization) of calcite crystals having the specific shape characteristics.