Mineral Characteristics of Some Soils of Puerto Rico

Abstract

Preliminary data are presented of some of the mineralogical characteristics of 41 soil series of Puerto Rico, which includes soils of three orders, 22 great soil groups occurring in seven physiographic provinces. Study of the constituent minerals of these soils show that there are present quartz, feldspars of the plagioclase series, and the clay minerals kaolin, illite, montmorillonite, and one called provisionally beidellite. The soils can be divided into two general groups, those with abundant feldspar and those where feldspar is absent or occurs only in traces. On the average, those soils which contain feldspar have a lower clay content, a higher total exchange capacity, and a higher productivity rating, where lack of rainfall or extreme slope are not factors, than those soils where feldspars are absent or occur only in traces. This appears to be independent of the great soil group, or province in which the soil series occur. It may be that the presence or abscence of feldspar in a soil is one of the indications of its potential fertility status.

Origin of Native Potassium in Alonso Soil

“…More recent work (10) concerning the mineral composition of the coarse fraction of Alonso confirmed the findings of Jeffries et al (7,8) that potassium-bearing minerals were not found in Alonso in the sand or silt fraction; also, that a high cation exchange capacity was detected. This suggested the possibility that native potassium in Alonso could originate from a clay mineral which escaped detection by techniques employed in previous investigations.…”

“…Using the X-ray spectroscopic method, Jeffries et al (7,8) 2 did not detect potassium-bearing minerals in either coarse or clay fraction of Alonso soil. Although they did not identify potassium feldspars in Alonso, they suggested the available potassium may originate from these minerals.…”

A Qualitative Mineral Analysis of the Coarse Fraction of an Alonso Soil

“…The X-ray diffraction angles were analysed by comparing their corresponding d-spacings with those of the X-ray powder data file, American Society for Testing Materials. An IBM 4 program was established to identify the minerals present and the IBM selections were always re-examined by visual inspections of the X-ray patterns.…”

“…Previous mineralogical analyses of Alonso (5,4) on fractions other than the clay have been reported to contain quartz in the very fine sand and silt fractions. No specific reference is made, however, to the quartz content in the coarser sand fractions.…”

“…During the course of a general mineralogical analysis performed on soil samples obtained from a typical Alonso profile by a Soil Conservation Service survey party, it was observed that the quartz content increased from the clay up to the fine sand fractions and then decreased toward the coarse sand. In previous work by Jeffries, Bonnet and Abrufia (3,4), no analysis was made for the presence of iron-bearing minerals. These are considered to be important mineralogical characteristics of ultisols and may be useful in the classification and interpretation of their properties.…”