The Ramson Cliff erratic -- optical mineralogy

Thanks to Paul Madgett for providing this image of the thin section obtained from a 1969 sample from the Ramson Cliff erratic. (Slide 72: PM7).  It may be referred to as an amphibolite or epidiorite.  Origin -- currently under debate.......

The purpose of this post is to provide some more visual material for independent scrutiny............

This is the technical description, presumably written by Rob Ixer:

Quote from Daw et al (2026), p 15:

The epidiorite is an amphibolitised microgabbro showing intergrowths between, up to 5.0 mm long, cloudy feldspar laths, altered brown-green mafics and skeletal opaques. Rare, bright green, up to 2 mm in diameter knots comprise secondary minerals.

In detail, clinopyroxene is extensively altered along cleavage planes and grain edges to pale brown and green amphibole. Plagioclase feldspar is slightly altered to fine-grained green amphibole, chlorite, white mica and probably very fine-grained clinozoisite. An ophitic relationship between feldspar and pyroxene is poorly developed. Opaques (probably magnetite or titanomagnetite) are mainly equant in shape, skeletal, and altered to titanite. Neither unaltered olivine nor pseudomorphs after it were recognised.

Secondary minerals include characteristic rounded segregations of deep green, pleochroic slightly zoned amphibole forming euhedral laths and equant crystals(many appear to be hexagonal in shape and show no cleavage) as infills around primary minerals. More commonly this generation of amphibole is enclosed within very pale green, low relief, chlorite showing blue interference colours and small lath-shaped phyllosilicate laths comprising chlorite-muscovite.

Trace amounts of radiating titanite and zoned apatite also may be present. These knots are petrographically distinctive.  

These images are from segments of the thin section -- two segments, each under plane-polarised light (PPL) and crossed polars (XPL):

Many thanks to Paul Madgett for these images, reproduced (rather badly!) from his slides.

Here are a couple of close-ups from a later sample, collected by Paul from the Ramson Cliff erratic in the 1970s:

The distinctive dark blue colour and slightly metallic appearance  is quite striking

Reference:

A REVIEW OF THE RAMSON CLIFF ERRATIC: EVIDENCE OF HIGH-LEVEL ICE FLOW? 

Tim Daw, Rob Ixer and Paul Madgett

Quaternary Newsletter 167, Feb 2026, pp 13-19

https://www.qra.org.uk/quaternary-newsletter/167-6-ramson-cliff-erratic/