福建平潭岛红色风沙色变机理探讨

A Discussion on Color Change Mechanism of Red Aeolian Sand in Pingtan Island,Fujian Province

平潭岛流水老红砂具有显著的红色、黄色色变现象。采集流水剖面27个样品,做粒度、电导率、色度、光谱等分析,研究表明:红色沙具有高红度值(a)、高黄度值(b)、低亮度值(L)的特点,而黄色沙a值低、b值低、L值高,色度参数a值和b值与红色的赤铁矿和黄色的针铁矿有关,红化是含铁硅酸盐矿物风化生成的针铁矿,在暖干气候下脱水转化成赤铁矿,使黏土和石英砂粒染红色;黄化或褪色是赤铁矿在相对湿润的气候条件下发生复杂的化学反应形成针铁矿,使沉积物呈黄色或褪色。红色沙和黄色沙交错反映了流水剖面的形成环境具有明显的干湿变化。

There occur color changes in red aerolian sand at Liushui profile in Pingtan Island. We take 27 samples from the profile and test their grain size, chroma and spectrum. It shows that red sands have the higher redness value （ a ）, higher yellowness value （ b ） and the lower lightness value （ L ）, but yellow sand lower a and b , higher L . The parameter a and b response to hematite and goethite that the reddening mechanism is silicate minerals containing ferrous iron weathered into goethite, and then goethite were dehydrated into hematite in warm and dry weather conditions, which made the clay and colorless quartz sand dyed red. The red sand and yellow sand staggered reflects the forming environment of Liushui profile has obvious climatic change between the arid and the humid.