The phrase "a rather large amount" is correct and usable in written English.
It can be used when describing a quantity that is significant or considerable, often in a more informal or conversational context.
Example: "The project required a rather large amount of resources to complete successfully."
Alternatives: "a considerable amount" or "a significant amount".
What this means is that a single rare event produced a rather large amount of this r-process material.
Things like moving the Shepparton football grounds growth cover to an area that had taken a rather large amount or wear.
Shales enriched in clay minerals contain a rather large amount of aluminum oxide, and during metamorphism of the shale mineral reactions and recrystallization occur.
The calcium process requires a rather large amount of reductant and gives low metal yields in the range of 75 80 percent.
Even though it's likely that the income from this measure would be less than $50bn if the concessions were removed, we're still talking a rather large amount of money – especially in the context of GST that is expected to raise $68.5bn in the same year.
Hence the need for the startup to be raising a rather large amount of early stage cash.
Thanksgiving and its aftermath has been a relaxing time for me, letting me charge my batteries for the rather large amount of work that I must do before the end of the year.
This analysis revealed presence of rather large amount of polystyrene in the final polymer product.
Until recently, people did not understand the rather large amount of toxins contributed to the environment by human activity such as excretion of drugs from our bodies, showering and bathing and disposal of unwanted or expired drugs and cosmetics in the sewers or trash systems.
However, we do not include a figure demonstrating it because it is shown in both cited papers ([ 13], [ 33] ) and we have already rather large amount of figures.
