GEM KNOWLEDGE · LABORATORY NOTES
Mosaic Quartz
A Brazilian stone whose pattern records several stages of mineral growth.
What the report found: Hydrothermal quartz, local hematite inclusions, dark chalcedony, later fine quartz and chalcedony infill, and an area interpreted as former opal now converted to chalcedony.
The specimen measures approximately 12.5 cm high. The report interprets possible fracturing between stages and suggests the later fractures may relate to dehydration of the former opal. The different colors and patches are a record of changing fluids and growth conditions, rather than one uniform quartz mass.
Our Brazilian sourcing has found very little of this material available in recent years. We have not confirmed whether its deposit is exhausted.
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Analytical Result Report Sample id: 9215 (Mosaic quartz from Brazil) Submitted by: K. Bitner Date submitted: Oct. 16, 2020 Date completed: Nov. 6, 2020 Operating conditions: JEOL JSM-6400 operated at 25 kV acceleration potential, 15 mm working distance, 15 degrees sample tilt, coated with 250 Å carbon. Using the X-ray fluorescence attachment with 35kv potental in conjunction with the EDS system. Fig. 1: Photograph of the six areas of thespecimen. Hegighht of the speciemn is about 12.5 cm. Table 1: Compositions of the different areas in the shiva (remainder is silicon) element Area 1 Area 2 Area 3 Area 4 Area 5 Area 6 Iron 6140 ppm 5150 ppm 400 ppm 650 ppm 380 ppm 370 ppm Manganese 360 ppm 390 ppm 220 ppm Titanium 420 ppm 360 ppm 250 ppm 2650 ppm 360 ppm Calcium 420 ppm 300 ppm 1.35 wt. % 280 ppm Potassium 1.36 wt. % 7200 ppm Aluminum 7400 ppm 2.16 wt. % 1.7 wt. % Summary of findings: This specimen recorded a lot of its history! It started out as a vein of hydrothermal quartz. Intergrown, in part euhedral crystals (the round tag with #3 sits right on top of a cross section of a quartz crystal! In some of the quartz crystals, fine-grained red hematite was included during crystal growth (area 5 in Fig. 1). Next was an infilling of dark, faintly banded chalcedony on the quartz crystals (area 3 in Fig. 1). This initial infilling was only a thin layer, but it was followed by finer-grained quartz with higher manganese and calcium content (areas 2 and 6 in Fig. 1). Note that in both areas potassium and aluminum are elevated, this is likely due to some clays such as illite or fine- grained sericite. It is possible that there was some fracturing of the vein contents before this infilling. This fracturing could have opened a pathway to those fluids. Infilling of the area 4 (Fig. 1) was likely next, this fluid brought much more calcium into the vein. The infilling is fine-grained, essentially chalcedony. The last steep was originally an opal infilling in area 1 which now has converted to chalcedony. The fracturing evident likely is a result of the opal dehydration. Date: November 6, 2020 Signature